Liquid crystal display device

ABSTRACT

A liquid crystal display device is provided, which includes a thin film transistor including an oxide semiconductor layer, a first electrode layer, a second electrode layer having an opening, a light-transmitting chromatic-color resin layer between the thin film transistor and the second electrode layer, and a liquid crystal layer. One of the first electrode layer and the second electrode layer is a pixel electrode layer which is electrically connected to the thin film transistor, and the other of the first electrode layer and the second electrode layer is a common electrode layer. The light-transmitting chromatic-color resin layer is overlapped with the pixel electrode layer and the oxide semiconductor layer of the thin film transistor.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a liquid crystal display device usingan oxide semiconductor and a method for manufacturing the same.

2. Description of the Related Art

As typically seen in a liquid crystal display device, a thin filmtransistor formed over a flat plate such as a glass substrate ismanufactured using amorphous silicon or polycrystalline silicon. A thinfilm transistor manufactured using amorphous silicon has low fieldeffect mobility, but can be formed over a larger glass substrate. Incontrast, a thin film transistor manufactured using polycrystallinesilicon has high field effect mobility, but needs a crystallization stepsuch as laser annealing and is not always suitable for a larger glasssubstrate.

In view of the foregoing, attention has been drawn to a technique formanufacturing a thin film transistor using an oxide semiconductor andapplying the thin film transistor to an electronic device or an opticaldevice. For example, Patent Document 1 and Patent Document 2 disclose atechnique by which a thin film transistor is manufactured using zincoxide or an In—Ga—Zn—O-based oxide semiconductor for an oxidesemiconductor film and such a transistor is used as a switching elementor the like of an image display device.

The thin film transistor in which a channel formation region is formedusing an oxide semiconductor has higher field effect mobility than athin film transistor using amorphous silicon. The oxide semiconductorfilm can be formed by a sputtering method or the like at a temperature300° C. or lower. Its manufacturing process is easier than that of athin film transistor using polycrystalline silicon.

The oxide semiconductor is a transparent semiconductor which transmitslight in a visible wavelength range; thus, it is said that use of theoxide semiconductor for a pixel of a display device makes it possible toprovide a high aperture ratio.

Such an oxide semiconductor is expected to be used for forming a thinfilm transistor on a glass substrate, a plastic substrate, or the like,and to be applied to a display device.

REFERENCE

-   [Patent Document 1] Japanese Published Patent Application No.    2007-123861-   [Patent Document 2] Japanese Published Patent Application No.    2007-096055

SUMMARY OF THE INVENTION

Thus, it is an object to provide a liquid crystal display device whichis suitable for a thin film transistor using an oxide semiconductor.

In a liquid crystal display device including thin film transistors eachincluding an oxide semiconductor layer, a film having a function ofattenuating the intensity of transmitting visible light is used for aninterlayer film which covers at least the oxide semiconductor layer. Thefilm having a function of attenuating the intensity of transmittingvisible light is a film having a transmittance of visible light lowerthan the oxide semiconductor layer. As the film having a function ofattenuating the intensity of transmitting visible light, a coloringlayer can be used, and a light-transmitting chromatic-color resin layeris preferable. Alternatively, in the interlayer film including alight-transmitting chromatic-color resin layer and a light-blockinglayer, the light-blocking layer may be used as a film having a functionof attenuating the intensity of transmitting visible light.

When a coloring layer which is a light-transmitting chromatic-colorresin layer is used as the interlayer film provided over a thin filmtransistor, the intensity of incident light on a semiconductor layer ofthe thin film transistor can be attenuated without reduction in anaperture ratio of a pixel. Accordingly, electric characteristics of thethin film transistor can be prevented from being varied due tophotosensitivity of the oxide semiconductor and can be stabilized.Further, the light-transmitting chromatic-color resin layer can functionas a color filter layer. In the case of providing a color filter layeron the counter substrate side, precise positional alignment of a pixelregion with an element substrate over which a thin film transistor isformed is difficult and accordingly there is a possibility that imagequality is degraded. Here, since the interlayer film is formed as thecolor filter layer directly on the element substrate side, the formationregion can be controlled more precisely and this structure is adjustableto a pixel with a fine pattern. In addition, one insulating layer canserve as both the interlayer film and the color filter layer, wherebythe process can be simplified and a liquid crystal display device can bemanufactured at low cost.

As a technique for realizing a wide viewing angle, a method is used inwhich a gray scale is controlled by generating an electric fieldapproximately parallel (i.e., in a lateral direction) to a substrate tomove liquid crystal molecules in a plane parallel to the substrate. Insuch a method, an electrode structure used in a fringe field switching(FFS) mode can be used.

In a horizontal electric field mode such as an FFS mode, a firstelectrode layer in a flat-plate shape (e.g., a pixel electrode layerwith which voltage is controlled per pixel) and a second electrode layerhaving an opening pattern (e.g., a common electrode layer with whichcommon voltage is applied to all pixels) are located below a liquidcrystal layer such that the second electrode layer is provided above thefirst electrode layer so as to overlap the first electrode layer. Byapplying an electric field between the pixel electrode layer and thecommon electrode layer, liquid crystal is controlled. An electric fieldin a lateral direction is applied to the liquid crystal, so that liquidcrystal molecules can be controlled using the electric field. That is,since the liquid crystal molecules can be controlled in a directionparallel to the substrates, a wide viewing angle can be obtained.Accordingly, a liquid crystal display device with improved viewing anglecharacteristics and higher image quality can be provided.

Chromatic colors are colors except achromatic colors such as black,gray, and white. The light-transmitting chromatic-color resin layer isformed using a material which transmits only light of a chromatic colorwhich the material is colored in so as to function as a color filter. Asa chromatic color, red, green, blue, or the like can be used.Alternatively, cyan, magenta, yellow, or the like may be used.“Transmitting only light of a chromatic color which a material iscolored in” means that light transmitted through the light-transmittingchromatic-color resin layer has a peak at the wavelength of thechromatic color light.

The thickness of the light-transmitting chromatic-color resin layer ispreferably controlled as appropriate in consideration of a relationbetween the concentration of the coloring material to be contained andlight transmittance, in order to make the light-transmittingchromatic-color resin layer function as a color filter layer. In thecase of forming the interlayer film by stacking a plurality of thinfilms, if at least one of the thin films is a light-transmittingchromatic-color resin layer, the interlayer film can function as a colorfilter.

In the case where the thickness varies depending on the chromatic colorsor in the case where there is surface unevenness due to a thin filmtransistor, an insulating layer which transmits light in a visiblewavelength range (so-called colorless and transparent insulating layer)may be stacked for planarization of the surface of the interlayer film.Improvement in planarization of the interlayer film allows favorablecoverage with a pixel electrode layer or a common electrode layer to beformed thereover and uniform gap (thickness) of a liquid crystal layer,whereby the visibility of the liquid crystal display device is increasedand higher image quality can be achieved.

When a light-blocking layer (black matrix) is used in the interlayerfilm provided over the thin film transistor, the light-blocking layercan block incident light on the semiconductor layer of the thin filmtransistor. Thus, electric characteristics of the thin film transistorcan be prevented from being varied due to photosensitivity of the oxidesemiconductor and can be stabilized. Further, the light-blocking layercan prevent light leakage to an adjacent pixel, which enables highercontrast and higher definition display. Therefore, high definition andhigh reliability of the liquid crystal display device can be achieved.

Accordingly, an element layer, a pixel electrode layer, a commonelectrode layer, and an interlayer film (the light-transmittingchromatic-color resin layer) are formed over the same substrate andsealed with a counter substrate which is opposite to the substrate withthe liquid crystal layer interposed therebetween. The pixel electrodelayer and the common electrode layer are located so as to be stackedwith an insulating film (or the interlayer film) interposedtherebetween. One of the pixel electrode layer and the common electrodelayer is formed in a lower part (a position far from the liquid crystallayer) and has a plate shape. On the other hand, the other electrodelayer is formed in an upper part (a position close to the liquid crystallayer) and has various opening patterns such as a pattern with a bendportion or a comb-like shape. In this specification, the electrode layerformed in a lower layer far from the liquid crystal layer (close to theelement substrate) is referred to as a first electrode layer, and thefirst electrode layer has a flat-plate shape. On the hand, the electrodelayer formed in an upper layer closed to the liquid crystal layer (farfrom the element substrate) is referred to as a second electrode layer,and the second electrode layer has an opening pattern (slit). In orderto generate an electric field between the pixel electrode layer and thecommon electrode layer, the electrode layers are located such that thefirst electrode layer in a flat-plate shape and the opening pattern(slit) of the second electrode layer overlap with each other.

In this specification, the opening pattern (slit) of the pixel electrodelayer or the common electrode layer includes a pattern of a comb-likeshape which has a partly-opened portion, in addition to a pattern whichhas an opening in a closed space.

In this specification, a substrate over which a thin film transistor, apixel electrode layer, a common electrode layer, and an interlayer filmare formed is referred to as an element substrate (a first substrate),and a substrate which is positioned opposite from the element substratewith a liquid crystal layer interposed therebetween is referred to as acounter substrate (a second substrate).

The light-blocking layer can be formed on either the counter substrateside or the element substrate side of the liquid crystal display device.Accordingly, improvement in contrast and stabilization of the thin filmtransistor can be achieved. When the light-blocking layer is formed in aregion corresponding to the thin film transistor (at least in a regionwhich overlaps with a semiconductor layer of the thin film transistor),electric characteristics of the thin film transistor can be preventedfrom being varied due to incident light from the counter substrate. Inthe case where the light-blocking layer is formed on the countersubstrate side, the light-blocking layer may be formed in a regioncorresponding to the thin film transistor (at least in a region whichcovers the semiconductor layer of the thin film transistor) with aliquid crystal layer interposed therebetween. In the case where thelight-blocking layer is formed on the element substrate side, thelight-blocking layer may be formed directly over the thin filmtransistor (at least in a region which covers the semiconductor layer ofthe thin film transistor) or formed over the thin film transistor withan insulating layer interposed therebetween.

In the case where the light-blocking layer is also provided on thecounter substrate side, there is a case where light from the elementsubstrate and light from the counter substrate toward the semiconductorlayer of the thin film transistor can be blocked by a light-blockingwiring layer, electrode layer, or the like. Thus, the light-blockinglayer need not always be formed to cover the thin film transistor.

An embodiment of the invention disclosed in this specification includesa thin film transistor in which an oxide semiconductor layer overlappingwith a gate electrode layer is a channel formation region, a firstelectrode layer in a flat-plate shape, a second electrode layer havingan opening pattern, an interlayer film provided between the thin filmtransistor and the second electrode layer, and a liquid crystal layerover the interlayer film, the first electrode layer, and the secondelectrode layer. One of the first electrode layer and the secondelectrode layer is a pixel electrode layer which is electricallyconnected to the thin film transistor, and the other electrode layer isa common electrode. The interlayer film is a light-transmittingchromatic-color resin layer having light transmittance lower than theoxide semiconductor layer. The light-transmitting chromatic-color resinlayer is provided so as to overlap with the pixel electrode layer andcover the oxide semiconductor layer.

Another embodiment of the invention disclosed in this specificationincludes a thin film transistor in which an oxide semiconductor layeroverlapping with a gate electrode layer is a channel formation region, afirst electrode layer in a flat-plate shape, a second electrode layerhaving an opening pattern, an interlayer film provided between the thinfilm transistor and the second electrode layer, and a liquid crystallayer over the interlayer film, the first electrode layer, and thesecond electrode layer. One of the first electrode layer and the secondelectrode layer is a pixel electrode layer which is electricallyconnected to the thin film transistor, and the other electrode layer isa common electrode layer. The interlayer film includes a light-blockinglayer and a light-transmitting chromatic-color resin layer having lighttransmittance lower than the oxide semiconductor layer. Thelight-blocking layer is provided to cover the oxide semiconductor layer.The light-transmitting chromatic-color resin layer is provided tooverlap with the pixel electrode layer.

In this specification, in the case where a liquid crystal display deviceis a light-transmitting liquid crystal display device (or asemi-transmissive liquid crystal display device) which performs displayby transmitting light from a light source, light is needed to betransmitted at least in the pixel region. Thus, all components providedin the pixel region through which light is transmitted: the firstsubstrate; the second substrate; and thin films included in an elementlayer, such as the pixel electrode layer, the common electrode layer,the insulating film, and the conductive film, have a property oftransmitting light in a visible wavelength range.

Note that the ordinal numbers such as “first” and “second” in thisspecification are used for convenience and do not denote the order ofsteps and the stacking order of layers. In addition, the ordinal numbersin this specification do not denote particular names which specify theinvention.

In this specification, a semiconductor device refers to all types ofdevices which can function by using semiconductor characteristics. Anelectro-optical device, a semiconductor circuit, and an electronicdevice are included in the category of all semiconductor devices.

In a liquid crystal display device which includes a thin film transistorformed by using an oxide semiconductor layer for a channel, aninterlayer film which covers at least the oxide semiconductor layer isformed using a material which attenuates the intensity of transmittingvisible light. Accordingly, operation characteristics of the thin filmtransistor can be stabilized without reduction in an aperture ratio.

Further, viewing angle characteristics are improved; thus, a liquidcrystal display device with higher image quality can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate a liquid crystal display device.

FIGS. 2A to 2D illustrate a method for manufacturing a liquid crystaldisplay device.

FIGS. 3A and 3B illustrate a liquid crystal display device.

FIGS. 4A and 4B illustrate a liquid crystal display device.

FIGS. 5A and 5B illustrate a liquid crystal display device.

FIGS. 6A and 6B illustrate a liquid crystal display device.

FIGS. 7A and 7B illustrate a liquid crystal display device.

FIGS. 8A to 8D illustrate electrode layers of a liquid crystal displaydevice.

FIGS. 9A and 9B illustrate a liquid crystal display device.

FIGS. 10A and 10B illustrate a liquid crystal display device.

FIGS. 11A and 11B illustrate a liquid crystal display device.

FIGS. 12A to 12C illustrate a liquid crystal display device.

FIG. 13A is an external view illustrating an example of a televisiondevice and FIG. 13B is an external view illustrating an example of adigital photo frame.

FIGS. 14A and 14B are external views illustrating examples of gamemachines.

FIGS. 15A and 15B are external views illustrating examples of mobilephones.

FIG. 16 illustrates a liquid crystal display module.

FIGS. 17A and 17B illustrate a liquid crystal display device.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will be described with reference to the accompanyingdrawings. However, the present invention is not limited to the followingdescription, and it will be easily understood by those skilled in theart that various changes and modifications can be made in modes anddetails without departing from the spirit and scope of the presentinvention. Therefore, the present invention should not be construed asbeing limited to the description of the following embodiments. Note thata common reference numeral refers to the same part or a part having asimilar function throughout the drawings in the structures describedbelow, and the description thereof is omitted.

Embodiment 1

A liquid crystal display device is described with reference to FIGS. 1Aand 1B.

FIG. 1A is a plan view of a liquid crystal display device andillustrates one pixel thereof. FIG. 1B is a cross-sectional view alongline X1 to X2 in FIG. 1A.

In FIG. 1A, a plurality of source wiring layers (including a wiringlayer 405 a) are provided to be in parallel to each other (extended in avertical direction in the drawing) and apart from each other. Aplurality of gate wiring layers (including a gate electrode layer 401)are provided to be extended in a direction generally perpendicular tothe source wiring layers (the horizontal direction in the drawing) andapart from each other. Common wiring layers (common electrode layers)are provided adjacent to the respective plurality of gate wiring layersand extended in a direction generally parallel to the gate wiringlayers, that is, in a direction generally perpendicular to the sourcewiring layers (the horizontal direction in the drawing). A roughlyrectangular space is surrounded by the source wiring layers, the commonwiring layers (common electrode layers), and the gate wiring layers. Inthis space, a pixel electrode layer and the common electrode layer ofthe liquid crystal display device are provided. A thin film transistor420 driving the pixel electrode layer is provided at the upper leftcorner in the drawing. A plurality of pixel electrode layers and thinfilm transistors are provided in matrix.

In the liquid crystal display device of FIGS. 1A and 1B, a secondelectrode layer 446 electrically connected to the thin film transistor420 functions as a pixel electrode layer, and a first electrode layer447 electrically connected to the common wiring layer functions as acommon electrode layer. Note that as shown in FIGS. 1A and 1B, the firstelectrode layer 447 also serves as the common wiring layer in the pixel;thus, adjacent pixels are electrically connected to each other with acommon electrode layer 409. Note that a capacitor is formed with thepixel electrode layer and the common electrode layer. Although thecommon electrode layer can operate in a floating state (an electricallyisolated state), the potential of the common electrode layer may be setto a fixed potential, preferably to a potential around a commonpotential (an intermediate potential of an image signal which istransmitted as data) in such a level as not to generate flickers.

A method in which the gray scale is controlled by generating an electricfield generally parallel (i.e., in a horizontal direction) to asubstrate to move liquid crystal molecules in a plane parallel to thesubstrate can be used. For such a method, an electrode structure used inan FFS mode illustrated in FIGS. 1A and 1B can be employed.

In a horizontal electric field mode as an FFS mode, the first electrodelayer in a flat-plate shape (e.g., a pixel electrode layer with whichvoltage is controlled per pixel) and the second electrode layer havingan opening pattern (e.g., a common electrode layer with which commonvoltage is applied to all pixels) are located below the liquid crystallayer, such that the second electrode layer is provided above the firstelectrode layer so as to overlap the first electrode layer. Thus, over afirst substrate 441, the first electrode layer and the second electrodelayer, one of which is a pixel electrode layer and the other of which isa common electrode layer, are formed, and the pixel electrode layer andthe common electrode layer are provided so as to be stacked with aninsulating film (or an interlayer insulating film) interposedtherebetween. One of the pixel electrode layer and the common electrodelayer is formed below the other one and has a flat-plate shape, and theother electrode layer is formed above the one and has various openingpatterns such as a pattern with a bend portion or a comb-like shape. Thefirst electrode layer 447 and the second electrode layer 446 do not havethe same shape or do not overlap with each other in order to generate anelectric field between the electrodes.

In this specification, the electrode layer formed in a lower layer farfrom the liquid crystal layer (close to the element substrate) is afirst electrode layer, and the first electrode layer has a flat-plateshape. On the other hand, the electrode layer formed in an upper layerclose to the liquid crystal layer (far from the element substrate) is asecond electrode layer, and the second electrode layer has an openingpattern (slit). The first electrode layer in a flat-plate shape and theopening patter (slit) of the second electrode layer overlap with eachother in order to generate an electric field between the pixel electrodelayer and the common electrode layer.

An electric field is added between the pixel electrode layer and thecommon electrode layer, so that liquid crystal is controlled. Anelectric field in a horizontal direction is applied to the liquidcrystal, so that liquid crystal molecules can be controlled using theelectric field. That is, the liquid crystal molecules aligned inparallel to the substrate can be controlled in a direction parallel tothe substrate, whereby a wide viewing angle is obtained.

Examples of the first electrode layers 447 and the second electrodelayers 446 are illustrated in FIGS. 8A to 8D. As shown in FIGS. 8A to8D, first electrode layers 447 a to 447 d and second electrode layers446 a to 446 d are disposed so as to overlap with each other, andinsulating films are formed between the first electrode layers 447 a to447 d and the second electrode layers 446 a to 446 d, so that the firstelectrode layers 447 a to 447 d and the second electrode layers 446 a to446 d are formed over different films.

As illustrated in top views of FIGS. 8A to 8D, the second electrodelayers 446 a to 446 d patterned in various shapes are formed over thefirst electrode layers 447 a to 447 d. In FIG. 8A, the second electrodelayer 446 a over the first electrode layer 447 a has a V-like shape. InFIG. 8B, the second electrode layer 446 b over the first electrode layer447 b has a concentric circular shape. In FIG. 8C, the second electrodelayer 446 c over the first electrode layer 447 c has a comb-like shapesuch that the electrodes are engaged with each other. In FIG. 8D, thesecond electrode layer 446 d over the first electrode layer 447 d has acomb-like shape.

The thin film transistor 420 is an inverted staggered thin filmtransistor which includes, over the first substrate 441 having aninsulating surface, the gate electrode layer 401, a gate insulatinglayer 402, a semiconductor layer 403, n⁺ layers 404 a and 404 b servingas source and drain regions, and the wiring layers 405 a and 405 bserving as source and drain electrode layers. The first electrode layer447 is formed in the same layer as the gate electrode layer 401 over thefirst substrate 441 and is a flat-shaped electrode layer in the pixel.

An insulating film 407 which covers the thin film transistor 420 and isin contact with the semiconductor layer 403 is provided. An interlayerfilm 413 is provided over the insulating film 407, and over theinterlayer film 413, the second electrode layer 446 having an openingpattern is formed. Thus, the first electrode layer 447 and the secondelectrode layer 446 are provided to overlap with each other with thegate insulating layer 402, the insulating film 407, and the interlayerfilm 413 interposed therebetween.

As for the interlayer film 413 in the liquid crystal display device ofFIGS. 1A and 1B, a light-transmitting chromatic-color resin layer 417which is a film having a function of attenuating the intensity oftransmittance visible light. The light-transmitting chromatic-colorresin layer 417 has transmittance of visible light lower than thesemiconductor layer 403 which is an oxide semiconductor layer.

When a coloring layer which is the light-transmitting chromatic-colorresin layer 417 is used as the interlayer film 413 provided over thethin film transistor 420, the intensity of incident light on thesemiconductor layer 403 of the thin film transistor 420 can beattenuated without reduction in an aperture ratio of a pixel.Accordingly, electric characteristics of the thin film transistor 420can be prevented from being varied due to photosensitivity of the oxidesemiconductor and can be stabilized. Further, the light-transmittingchromatic-color resin layer 417 can function as a color filter layer. Inthe case of providing the color filter layer on the counter substrateside, precise positional alignment of a pixel region with an elementsubstrate over which the thin film transistor is formed is difficult,and accordingly there is a possibility that image quality is degraded.Here, since the interlayer film is formed as the color filter layerdirectly on the element substrate side, the formation region can becontrolled more precisely and this structure is adjustable to a pixelwith a fine pattern. In addition, one insulating layer serves as boththe interlayer film and the color filter layer, whereby the process canbe simplified and a liquid crystal display device can be manufactured atlow cost.

Chromatic colors are colors except achromatic colors such as black,gray, and white. The coloring layer is formed using a material whichtransmits only light of a chromatic color which the material is coloredin so as to function as the color filter. As chromatic color, red,green, blue, or the like can be used. Alternatively, cyan, magenta,yellow, or the like may also be used. “Transmitting only light of achromatic color which a material is colored in” means that lighttransmitted through the coloring layer has a peak at the wavelength ofthe chromatic color light.

The thickness of the light-transmitting chromatic-color resin layer ispreferably controlled as appropriate in consideration of a relationbetween the concentration of the coloring material to be contained andlight transmittance, in order to make the light-transmittingchromatic-color resin layer function as a color filter layer. In thecase of forming the interlayer film by stacking a plurality of thinfilms, if at least one of the thin films is a light-transmittingchromatic-color resin layer, the interlayer film can function as a colorfilter.

In the case where the thickness of the light-transmittingchromatic-color resin layer differs in accordance with the chromaticcolors or in the case where there is surface unevenness due to alight-blocking layer or the thin film transistor, an insulating layerwhich transmits light in a visible wavelength range (so-called colorlessand transparent insulating layer) may be stacked for planarization ofthe surface of the interlayer film. Improvement in planarization of theinterlayer film allows favorable coverage with the pixel electrode layeror the common electrode layer to be formed thereover and uniform gap(thickness) of the liquid crystal layer, whereby the visibility of theliquid crystal display device is increased and higher image quality canbe achieved.

As formation of the light-transmitting chromatic-color resin layer 417,a light-transmitting organic resin, a chromatic pigment, or a dye can beused, and an organic resin in which a pigment, a dye, or the like ismixed may be used. As the light-transmitting organic resin, aphotosensitive or non-photosensitive resin can be used. Use of thephotosensitive organic resin layer makes it possible to reduce thenumber of resist masks; thus, the steps are simplified, which ispreferable. In addition, since a contact hole formed in the interlayerfilm has an opening shape with a curvature, coverage with a film such asan electrode layer formed in the contact hole can be improved.

There is no particular limitation on the formation method of theinterlayer film 413 (the light-transmitting chromatic-color resin layer417). In accordance with the material, a wet method such as spincoating, dip coating, spray coating, or droplet discharging (e.g., inkjetting, screen printing, or offset printing) may be performed, and theformed film may be patterned into a desired shape by an etching method(dry etching or wet etching method) if necessary.

A liquid crystal layer 444 is provided over the first electrode layer447 and the second electrode layer 446 and sealed with a secondsubstrate 442 which is a counter substrate.

The first substrate 441 and the second substrate 442 arelight-transmitting substrates and are provided with a polarizing plate443 a and a polarizing plate 443 b respectively on their outer sides(the sides opposite from the side where the liquid crystal layer 444 isprovided).

The first electrode layer 447 and the second electrode layer 446 can beformed using a light-transmitting conductive material such as indiumoxide containing tungsten oxide, indium zinc oxide containing tungstenoxide, indium oxide containing titanium oxide, indium tin oxidecontaining titanium oxide, indium tin oxide (hereinafter referred to asITO), indium zinc oxide, or indium tin oxide to which silicon oxide isadded.

A conductive composition containing a conductive high molecule (alsoreferred to as a conductive polymer) can be used to form the firstelectrode layer 447 and the second electrode layer 446. The pixelelectrode formed using the conductive composition preferably has a sheetresistance of 10000 Ω/square or less and a transmittance of 70% or moreat a wavelength of 550 nm. Furthermore, the resistivity of theconductive high molecule contained in the conductive composition ispreferably 0.1 Ω·cm or less.

As the conductive high molecule, a so-called 7 c-electron conjugatedconductive polymer can be used. For example, it is possible to usepolyaniline or a derivative thereof, polypyrrole or a derivativethereof, polythiophene or a derivative thereof, or a copolymer of two ormore kinds of them.

An insulating film serving as a base film may be provided between thefirst substrate 441, and the gate electrode layer 401 and the firstelectrode layer 447. The base film functions to prevent diffusion of animpurity element from the first substrate 441 and can be formed usingone film or stacked films selected from a silicon nitride film, asilicon oxide film, a silicon nitride oxide film, and a siliconoxynitride film. The gate electrode layer 401 can be formed to have asingle-layer structure or a stacked structure using a metal materialsuch as molybdenum, titanium, chromium, tantalum, tungsten, aluminum,copper, neodymium, or scandium or an alloy material which contains anyof these materials as its main component. By using a light-blockingconductive film as the gate electrode layer 401, light from a backlight(light emitted through the first substrate 441) can be prevented fromentering the semiconductor layer 403.

For example, as a two-layer structure of the gate electrode layer 401,the following structures are preferable: a two-layer structure of analuminum layer and a molybdenum layer stacked thereover, a two-layerstructure of a copper layer and a molybdenum layer stacked thereover, atwo-layer structure of a copper layer and a titanium nitride layer or atantalum nitride layer stacked thereover, and a two-layer structure of atitanium nitride layer and a molybdenum layer. As a three-layerstructure, a stack of a tungsten layer or a tungsten nitride layer, alayer of an alloy of aluminum and silicon or an alloy of aluminum andtitanium, and a titanium nitride layer or a titanium layer ispreferable.

The gate insulating layer 402 can be formed to have a single-layerstructure or a stacked structure using a silicon oxide layer, a siliconnitride layer, a silicon oxynitride layer, or a silicon nitride oxidelayer by a plasma CVD method, a sputtering method, or the like.Alternatively, the gate insulating layer 402 can be formed using asilicon oxide layer by a CVD method using an organosilane gas. As theorganosilane gas, a silicon-containing compound such astetraethoxysilane (TEOS: chemical formula, SKOC₂H₅)₄), tetramethylsilane(TMS: chemical formula, Si(CH₃)₄), tetramethylcyclotetrasiloxane(TMCTS), octamethylcyclotetrasiloxane (OMCTS), hexamethyldisilazane(HMDS), triethoxysilane (SiH(OC₂H₅)₃), or trisdimethylaminosilane(SiH(N(CH₃)₂)₃) can be used.

It is preferable that reverse sputtering in which an argon gas isintroduced to generate plasma be performed before the formation of theoxide semiconductor film used as the semiconductor layer 403 in order toremove dust attached to a surface of the gate insulating layer. Notethat instead of an argon atmosphere, a nitrogen atmosphere, a heliumatmosphere, or the like may be used. Alternatively, an argon atmosphereto which oxygen, hydrogen, N₂O, or the like is added may be used.Further alternatively, an argon atmosphere to which Cl₂, CF₄, or thelike is added may be used.

In this specification, a thin film represented by InMO₃(ZnO)_(m) (m>0)is preferably used as an oxide semiconductor. In the thin filmtransistor 420, a thin film represented by InMO₃(ZnO)_(m) (m>0) isformed, and the thin film is used as the semiconductor layer 403. Notethat M denotes one or more of metal elements selected from gallium (Ga),iron (Fe), nickel (Ni), manganese (Mn), and cobalt (Co). In addition toa case where only Ga is contained as M, there is a case where Ga and theabove metal elements other than Ga are contained as M, for example, Mcontains Ga and Ni or Ga and Fe. Moreover, in the oxide semiconductor,in some cases, a transition metal element such as Fe or Ni or an oxideof the transition metal is contained as an impurity element in additionto a metal element contained as M. For example, an In—Ga—Zn—O-basednon-single-crystal film can be used.

In the case where M is gallium (Ga) in the InMO₃(ZnO)_(m) (m>0) film(layer), this thin film is referred to as an In—Ga—Zn—O-basednon-single-crystal film in this specification. Even in the case whereafter film formation by sputtering using a target ofIn₂O₃:Ga₂O₃:ZnO=1:1:1, the In—Ga—Zn—O-based non-single-crystal film issubjected to heat treatment at 200° C. to 500° C., typically 300° C. to400° C. for 10 minutes to 100 minutes, an amorphous structure isobserved in the In—Ga—Zn—O-based non-single-crystal film by X-raydiffraction (XRD) spectrometry. Further, a thin film transistor havingelectric characteristics such as an on/off ratio of 10⁹ or higher andmobility of 10 or higher at a gate voltage of ±20 V can be manufactured.In addition, the In—Ga—Zn—O-based non-single-crystal film formed bysputtering has photosensitivity at a wavelength of 450 nm or less.

The semiconductor layer 403 and the n⁺ layers 404 a and 404 b serving assource and drain regions can be formed using an In—Ga—Zn—O-basednon-single-crystal film. The n⁺ layers 404 a and 404 b are oxidesemiconductor layers having a resistance lower than the semiconductorlayer 403. For example, the n⁺ layers 404 a and 404 b have n-typeconductivity and an activation energy (ΔE) of from 0.01 eV to 0.1 eVinclusive. The n⁺ layers 404 a and 404 b are In—Ga—Zn—O-basednon-single-crystal films and include at least an amorphous component.The n⁺ layers 404 a and 404 b may include crystal grains (nanocrystals)in an amorphous structure. These crystal grains (nanocrystals) in the n⁺layers 404 a and 404 b each have a diameter of 1 nm to 10 nm, typicallyabout 2 nm to 4 nm.

Provision of the n⁺ layers 404 a and 404 b can make a good junctionbetween the wiring layers 405 a and 405 b which are metal layers and thesemiconductor layer 403 which is an oxide semiconductor layer, whichallows higher thermal stability than in the case of providing Schottkyjunction. In addition, willing provision of the n⁺ layer is effective insupplying carriers to the channel (on the source side), stably absorbingcarriers from the channel (on the drain side), or preventing aresistance component from being formed at an interface between thewiring layer and the semiconductor layer. Moreover, since resistance isreduced, high mobility can be ensured even with a high drain voltage.

A first In—Ga—Zn—O-based non-single-crystal film used as thesemiconductor layer 403 is formed under deposition conditions differentfrom those for formation of a second In—Ga—Zn—O based non-single-crystalfilm which is used as the n⁺ layers 404 a and 404 b. For example, a flowrate ratio of an oxygen gas to an argon gas in formation condition ofthe first In—Ga—Zn—O-based non-single-crystal film is made higher than aflow rate ratio of an oxygen gas to an argon gas in formation conditionof the second In—Ga—Zn—O-based non-single-crystal film. Specifically,the second In—Ga—Zn—O-based non-single-crystal film is formed in a raregas (e.g., argon or helium) atmosphere (or an atmosphere containing anoxygen gas of 10% or lower and an argon gas containing 90% or higher),and the first In—Ga—Zn—O-based non-single-crystal film is formed in anoxygen atmosphere (or an atmosphere in which a flow rate of oxygen gasis equal to or higher than a flow rate of argon gas).

For example, the first In—Ga—Zn—O-based non-single-crystal film used asthe semiconductor layer 403 is formed under the conditions where theoxide semiconductor target including In, Ga, and Zn (composition ratiois In₂O₃:Ga₂O₃:ZnO=1:1:1) with a diameter of 8 inches is used, thedistance between the substrate and the target is set at 170 mm, thepressure is set at 0.4 Pa, and the direct current (DC) power supply isset at 0.5 kW. Note that a pulse direct current (DC) power supply ispreferable because dust can be reduced and the film thickness can beuniform. The thickness of the first In—Ga—Zn—O-based non-single-crystalfilm is set to 5 nm to 200 nm.

On the other hand, the second In—Ga—Zn—O-based non-single-crystal filmused as the n⁺ layers 404 a and 404 b is formed by a sputtering methodusing the target (In₂O₃:Ga₂O₃:ZnO=1:1:1), under the conditions where thepressure is set at 0.4 Pa, the power is 500 W, the depositiontemperature is room temperature, and an argon gas is introduced at aflow rate of 40 sccm. An In—Ga—Zn—O based non-single-crystal filmincluding crystal grains with a size of 1 nm to 10 nm immediately afterthe film formation is formed in some cases. Note that it can be saidthat the presence or absence of crystal grains or the density of crystalgrains can be adjusted and the diameter size can be adjusted within therange of 1 nm to 10 nm by appropriate adjustment of the reactivesputtering deposition conditions such as the composition ratio in thetarget, the film deposition pressure (0.1 to 2.0 Pa), the power (250 Wto 3000 W: 8 inches ϕ), the temperature (room temperature to 100° C.),or the like. The second In—Ga—Zn—O-based non-single-crystal film has athickness of 5 nm to 20 nm. Needless to say, when the film includescrystal grains, the size of the crystal grains does not exceed thethickness of the film. The thickness of the second In—Ga—Zn—O-basednon-single-crystal film is 5 nm.

Examples of a sputtering method include an RF sputtering method in whicha high-frequency power source is used as a sputtering power source, a DCsputtering method, and a pulsed DC sputtering method in which a bias isapplied in a pulsed manner. An RF sputtering method is mainly used inthe case where an insulating film is formed, and a DC sputtering methodis mainly used in the case where a metal film is formed.

In addition, there is also a multi-source sputtering apparatus in whicha plurality of targets of different materials can be set. With themulti-source sputtering apparatus, films of different materials can beformed to be stacked in the same chamber, or a film of plural kinds ofmaterials can be formed by electric discharge at the same time in thesame chamber.

Further, as a sputtering apparatus, there are a sputtering apparatusprovided with a magnet system inside the chamber and used for amagnetron sputtering method, and a sputtering apparatus used for an ECRsputtering method in which plasma is generated with the use of not glowdischarge but microwaves is used.

In addition, as a film formation method by sputtering, there are also areactive sputtering method in which a target substance and a sputteringgas component are chemically reacted with each other during filmformation to form a thin compound film thereof, and a bias sputteringmethod in which voltage is also applied to a substrate during filmformation.

In the manufacturing process of the semiconductor layer, the n⁺ layers,and the wiring layers, an etching step is used to process thin filmsinto desired shapes. Dry etching or wet etching can be used for theetching step.

As an etching gas used for dry etching, a gas containing chlorine (achlorine-based gas such as chlorine (Cl₂), boron chloride (BCl₃),silicon chloride (SiCl₄), or carbon tetrachloride (CCl₄)) is preferablyused.

Alternatively, a gas containing fluorine (a fluorine-based gas such ascarbon tetrafluoride (CF₄), sulfur fluoride (SF₆), nitrogen fluoride(NF₃), or trifluoromethane (CHF₃)), hydrogen bromide (HBr), oxygen (O₂),any of these gases to which a rare gas such as helium (He) or argon (Ar)is added, or the like can be used.

As an etching apparatus used for dry etching, an etching apparatus thatuses reactive ion etching (RIE), or a dry etching apparatus that uses ahigh-density plasma source such as an electron cyclotron resonance (ECR)source or an inductively coupled plasma (ICP) source can be used. Assuch a dry etching apparatus with which uniform discharge can be easilyobtained over a large area as compared to an ICP etching apparatus,there is an enhanced capacitively coupled plasma (ECCP) mode etchingapparatus in which an upper electrode is grounded, a high-frequencypower source of 13.56 MHz is connected to a lower electrode, and furthera low-frequency power source of 3.2 MHz is connected to the lowerelectrode. This ECCP mode etching apparatus can be used even in the casewhere a substrate having the size exceeding 3 meters of the tenthgeneration is used, for example.

In order to etch the films into desired shapes, etching conditions(e.g., the amount of electric power applied to a coiled electrode, theamount of electric power applied to an electrode on a substrate side, orthe electrode temperature on the substrate side) are controlled asappropriate.

As an etchant used for wet etching, a mixed solution of phosphoric acid,acetic acid, and nitric acid, an ammonia peroxide mixture (hydrogenperoxide:ammonia:water=5:2:2), or the like can be used. Alternatively,ITO-07N (produced by Kanto Chemical Co., Inc.) may be used.

The etchant after the wet etching is removed by cleaning, together withthe etched material. The waste liquid of the etchant including theetched material may be purified so that the included material is reused.If a material such as indium included in the oxide semiconductor layeris collected from the waste liquid of the etching and reused, resourcescan be used effectively and cost can be reduced.

In order to etch the films into desired shapes, etching conditions(e.g., etchant, etching time, temperature, or the like) are controlledas appropriate in accordance with the material.

As a material of the wiring layers 405 a and 405 b, an element selectedfrom Al, Cr, Ta, Ti, Mo, and W, an alloy containing any of the elementsas its component, an alloy containing any of the elements incombination, and the like can be given. Further, in the case ofperforming heat treatment at 200° C. to 600° C., the conductive filmpreferably has heat resistance against such heat treatment. Since Alitself has disadvantages such as low heat resistance and a tendency tobe corroded, it is used in combination with a conductive material havingheat resistance. As a conductive material having heat resistance whichis combined with Al, an element selected from titanium (Ti), tantalum(Ta), tungsten (W), molybdenum (Mo), chromium (Cr), neodymium (Nd), orscandium (Sc), or an alloy including any of the elements, an alloy filmincluding a combination of such elements, or a nitride film includingany of the elements can be used.

The gate insulating layer 402, the semiconductor layer 403, the n⁺layers 404 a and 404 b, and the wiring layers 405 a and 405 b may beformed in succession without being exposed to air. By successiveformation without exposure to air, each interface between the stackedlayers can be formed without being contaminated by atmosphericcomponents or contaminating impurities contained in air; therefore,variation in characteristics of the thin film transistor can be reduced.

Note that the semiconductor layer 403 is partly etched so as to have agroove (a depressed portion).

The semiconductor layer 403 and the n⁺ layers 404 a and 404 b arepreferably subjected to heat treatment at 200° C. to 600° C., typically300° C. to 500° C. For example, heat treatment is performed for 1 hourat 350° C. in a nitrogen atmosphere. By this heat treatment,rearrangement at the atomic level is caused in the In—Ga—Zn—O basedoxide semiconductor which forms the semiconductor layer 403 and the n⁺layers 404 a and 404 b. This heat treatment (also includingphoto-annealing or the like) is important in that the distortion thatinterrupts carrier transfer in the semiconductor layer 403 and the n⁺layers 404 a and 404 b can be reduced. Note that there is no particularlimitation on when to perform the heat treatment, as long as it isperformed after the semiconductor layer 403 and the n⁺ layers 404 a and404 b are formed.

In addition, oxygen radical treatment may be performed on the exposeddepression portion of the semiconductor layer 403. The radical treatmentis preferably performed in an atmosphere of O₂ or N₂O, or an atmosphereof N₂, He, Ar, or the like which includes oxygen. Alternatively, anatmosphere obtained by adding Cl₂ or CF₄ to the above atmosphere may beused. Note that the radical treatment is preferably performed with nobias voltage applied to the first substrate 441 side.

Note that there is no particular limitation on a structure of the thinfilm transistor formed in the liquid crystal display device. The thinfilm transistor may have a single-gate structure in which one channelformation region is formed, a double-gate structure in which two channelformation regions are formed, or a triple-gate structure in which threechannel formation regions are formed. In addition, the transistor in theperipheral driver circuit region may also have a single-gate structure,a double-gate structure, or a triple-gate structure.

The thin film transistor may have a top-gate structure (e.g., astaggered structure or a coplanar structure), a bottom-gate structure(e.g., an inverted-staggered structure or an inverted-coplanarstructure), a dual-gate structure including two gate electrode layersprovided above and below a channel region each with a gate insulatingfilm interposed therebetween, or other structures.

An alignment film or an optical film such as a polarizing plate, aretardation plate, or an anti-reflection film is provided asappropriate. For example, circular polarization by the polarizing plateand the retardation plate may be used. In addition, a backlight, a sidelight, or the like may be used as a light source.

The insulating film 407 covering the thin film transistor 420 can beformed using an inorganic insulating film or organic insulating filmformed by a wet method or a dry method. For example, the insulating film407 can be formed by a CVD method, a sputtering method, or the like,using a silicon nitride film, a silicon oxide film, a silicon oxynitridefilm, an aluminum oxide film, a tantalum oxide film, or the like.Alternatively, an organic material such as acrylic, polyimide,benzocyclobutene, polyamide, or an epoxy resin can be used. Other thansuch organic materials, it is also possible to use a low-dielectricconstant material (a low-k material), a siloxane-based resin, PSG(phosphosilicate glass), BPSG (borophosphosilicate glass), or the like.

Note that a siloxane-based resin is a resin formed from a siloxane-basedmaterial as a starting material and having the bond of Si—O—Si. Asiloxane-based resin may include, as a substituent, an organic group(e.g., an alkyl group, and an aryl group) or a fluoro group. The organicgroup may include a fluoro group. A siloxane-based resin is applied by acoating method and baked; thus, the insulating film 407 can be formed.

Alternatively, the insulating film 407 may be formed by stacking pluralinsulating films formed using any of these materials. For example, theinsulating film 407 may have such a structure that an organic resin filmis stacked over an inorganic insulating film.

As a liquid crystal material of the liquid crystal layer 444, variouskinds of liquid crystal can be used, and lyotropic liquid crystal,thermotropic liquid crystal, low molecular liquid crystal, highmolecular liquid crystal, discotic liquid crystal, ferroelectric liquidcrystal, anti-ferroelectric liquid crystal, or the like may be selectedas appropriate to be used.

In this specification, in the case where a liquid crystal display deviceis a light-transmitting liquid crystal display device (or asemi-transmissive liquid crystal display device) which performs displayby transmitting light from a light source, light is needed to betransmitted at least in the pixel region. Thus, all components providedin the pixel region through which light is transmitted: the firstsubstrate; the second substrate; and thin films included in an elementlayer, such as the pixel electrode layer, the common electrode layer,the insulating film, and the conductive film have a property oftransmitting light in a visible wavelength range.

As for the first substrate 441 and the second substrate 442, a glasssubstrate of barium borosilicate glass, aluminoborosilicate glass, orthe like; a quartz substrate; a plastic substrate; or the like can beused.

Further, by use of a resist mask having regions with plural thicknesses(typically, two different thicknesses) which is formed using amulti-tone mask, the number of resist masks can be reduced, resulting insimplified process and lower costs.

Improvement in contrast and viewing angle characteristics enables aliquid crystal display device with higher image quality to be supplied.Further, such a liquid crystal display device can be manufactured at lowcost with high productivity.

Further, characteristics of the thin film transistor can be stabilized;thus, reliability of the liquid crystal display device can be improved.

Embodiment 2

Another mode of a liquid crystal display device is illustrated in FIGS.3A and 3B. Specifically, an example of a liquid crystal display deviceis described, in which a first electrode layer in a flat-plate shapeformed in a lower layer is used as a pixel electrode layer, and a secondelectrode layer having an opening pattern formed in an upper layer isused as a common electrode layer. Note that components in common withthose in Embodiment 1 can be formed using the similar material and thesimilar manufacturing method, and detailed description of the sameportions and portions which have similar functions is omitted.

FIG. 3A is a plan view of a liquid crystal display device andillustrates one pixel thereof. FIG. 3B is a cross-sectional view alongline X1 to X2 in FIG. 3A.

In FIG. 3A, a plurality of source wiring layers (including the wiringlayer 405 a) are provided in parallel to each other (extended in avertical direction in the drawing) and apart from each other. Aplurality of gate wiring layers (including the gate electrode layer 401)are provided apart from each other and extended in a direction generallyperpendicular to the source wiring layers (a horizontal direction in thedrawing). Common wiring layers 408 are provided adjacent to therespective plurality of gate wiring layers and extended in a directiongenerally parallel to the gate wiring layers, that is, in a directiongenerally perpendicular to the source wiring layers (a horizontaldirection in the drawing). A roughly rectangular space is surrounded bythe source wiring layers, the common wiring layers 408, and the gatewiring layers. In this space, a pixel electrode layer and a commonelectrode layer of the liquid crystal display device are provided. Thethin film transistor 420 for driving the pixel electrode layer isprovided at the upper left corner in the drawing. A plurality of pixelelectrode layers and thin film transistors are provided in matrix.

In FIGS. 3A and 3B, the first electrode layer 447 electrically connectedto the thin film transistor 420 functions as a pixel electrode layer,and the second electrode layer 446 electrically connected to the commonwiring layer functions as a common electrode layer. The first electrodelayer 447 is electrically connected to the thin film transistor 420through a contact hole formed in the gate insulating layer 402. Thesecond electrode layer 446 is electrically connected to the commonwiring layer 408 through a contact hole formed in the gate insulatinglayer 402, the insulating film 407, and the interlayer film 413.

When a coloring layer which is the light-transmitting chromatic-colorresin layer 417 is used as the interlayer film 413 provided over thethin film transistor 420, the intensity of incident light on thesemiconductor layer 403 of the thin film transistor 420 can beattenuated without reduction in an aperture ratio of a pixel.Accordingly, electric characteristics of the thin film transistor 420can be prevented from being varied due to photosensitivity of the oxidesemiconductor and can be stabilized. Further, the light-transmittingchromatic-color resin layer 417 can function as a color filter layer. Inthe case of providing the color filter layer on the counter substrateside, precise positional alignment of a pixel region with an elementsubstrate over which the thin film transistor is formed is difficult,and accordingly there is a possibility that image quality is degraded.Here, since the interlayer film is formed as the color filter layerdirectly on the element substrate side, the formation region can becontrolled more precisely and this structure is adjustable to a pixelwith a fine pattern. In addition, one insulating layer serves as boththe interlayer film and the color filter layer, whereby the process canbe simplified and a liquid crystal display device can be manufactured atlow cost.

Improvement in contrast and viewing angle characteristics enables aliquid crystal display device with higher image quality to be supplied.Further, such a liquid crystal display device can be manufactured at lowcost with high productivity.

Further, characteristics of the thin film transistor can be stabilized;thus, reliability of the liquid crystal display device can be improved.

Embodiment 3

Other modes of liquid crystal display devices are illustrated in FIGS.4A and 4B and FIGS. 7A and 7B. Specifically, structural examples aredescribed, in each of which a first electrode layer is provided above athin film transistor. Note that components in common with those inEmbodiments 1 and 2 can be formed using the similar material and thesimilar manufacturing method, and detailed description of the sameportions and portions which have similar functions is omitted.

FIG. 4A and FIG. 7A are each a plan view of a liquid crystal displaydevice and each illustrate one pixel. FIG. 4B and FIG. 7B arecross-sectional views of FIG. 4A and FIG. 7A along line X1 to X2,respectively.

In each plan view of FIG. 4A and FIG. 7A, in a manner similar toEmbodiment 2, a plurality of source wiring layers (including the wiringlayer 405 a) are provided in parallel to each other (extended in avertical direction in the drawing) and apart from each other. Aplurality of gate wiring layers (including the gate electrode layer 401)are provided apart from each other and extended in a direction generallyperpendicular to the source wiring layers (a horizontal direction in thedrawing). The common wiring layers 408 are provided adjacent to therespective plurality of gate wiring layers and extended in a directiongenerally parallel to the gate wiring layers, that is, in a directiongenerally perpendicular to the source wiring layers (a horizontaldirection in the drawing). A roughly rectangular space is surrounded bythe source wiring layers, the common wiring layers 408, and the gatewiring layers. In this space, a pixel electrode layer and a commonelectrode layer of the liquid crystal display device are provided. Thethin film transistor 420 for driving the pixel electrode layer isprovided at the upper left corner in the drawing. A plurality of pixelelectrode layers and thin film transistors are provided in matrix.

In each liquid crystal display device of FIG. 4B and FIG. 7B, the firstelectrode layer 447 in a flat-plate shape which is electricallyconnected to the thin film transistor 420 functions as a pixel electrodelayer. The second electrode layer 446 having an opening pattern which iselectrically connected to the common wiring layer 408 functions as acommon electrode layer.

In FIGS. 4A and 4B, the first electrode layer 447 is formed over theinsulating film 407, the interlayer film 413 is stacked over the firstelectrode layer 447, and the second electrode layer 446 is formed overthe interlayer film 413. Note that in FIGS. 4A and 4B, a capacitor isformed with the first electrode layer and the common electrode layer.

In FIGS. 7A and 7B, the first electrode layer 447 is formed over theinterlayer film 413, an insulating film 416 is stacked over the firstelectrode layer 447, and the second electrode layer 446 is formed overthe insulating film 416. Note that in FIGS. 7A and 7B, a capacitor isformed with the first electrode layer and the common electrode layer.

When a coloring layer which is the light-transmitting chromatic-colorresin layer 417 is used as the interlayer film 413 provided over thethin film transistor 420, the intensity of incident light on thesemiconductor layer 403 of the thin film transistor 420 can beattenuated without reduction in an aperture ratio of a pixel.Accordingly, electric characteristics of the thin film transistor 420can be prevented from being varied due to photosensitivity of the oxidesemiconductor and can be stabilized. Further, the light-transmittingchromatic-color resin layer 417 can function as a color filter layer. Inthe case of providing the color filter layer on the counter substrateside, precise positional alignment of a pixel region with an elementsubstrate over which the thin film transistor is formed is difficult,and accordingly there is a possibility that image quality is degraded.Here, since the interlayer film is formed as the color filter layerdirectly on the element substrate side, the formation region can becontrolled more precisely and this structure is adjustable to a pixelwith a fine pattern. In addition, one insulating layer can serve as boththe interlayer film and the color filter layer, whereby the process canbe simplified and a liquid crystal display device can be manufactured atlow cost.

Improvement in contrast and viewing angle characteristics enables aliquid crystal display device with higher image quality to be supplied.Further, such a liquid crystal display device can be manufactured at lowcost with high productivity.

Further, characteristics of the thin film transistor can be stabilized;thus, reliability of the liquid crystal display device can be improved.

Embodiment 4

A liquid crystal display device including a light-blocking layer (blackmatrix) is described with reference to FIGS. 5A and 5B.

The liquid crystal display device illustrated in FIGS. 5A and 5B showsan example in which a light-blocking layer 414 is further added on thesecond substrate (counter substrate) 442 side to the liquid crystaldisplay device illustrated in FIGS. 1A and 1B of Embodiment 1.Therefore, components in common with those in Embodiment 1 can be formedusing a similar material and a similar manufacturing method, anddetailed description of the same portions and portions having similarfunctions is omitted.

FIG. 5A is a plan view of a liquid crystal display device, and FIG. 5Bis a cross-sectional view along line X1 to X2 in FIG. 5A. Note that theplan view of FIG. 5A illustrates only the element substrate side and thecounter substrate side is not illustrated.

The light-blocking layer 414 is formed on the liquid crystal layer 444side of the second substrate 442 and an insulating layer 415 is formedas a planarization film. The light-blocking layer 414 is preferablyformed in a region corresponding to the thin film transistor 420 (aregion which overlaps with the semiconductor layer of the thin filmtransistor) with the liquid crystal layer 444 interposed therebetween.The first substrate 441 and the second substrate 442 are firmly attachedto each other with the liquid crystal layer 444 interposed therebetweenso that the light-blocking layer 414 is positioned to cover at least anupper portion of the semiconductor layer 403 of the thin film transistor420.

The light-blocking layer 414 has transmittance of visible light lowerthan the semiconductor layer 403 which is an oxide semiconductor layer.

The light-blocking layer 414 is formed using a light-blocking materialthat reflects or absorbs light. For example, a black organic resin canbe used, which can be formed by mixing a black resin of a pigmentmaterial, carbon black, titanium black, or the like into a resinmaterial such as photosensitive or non-photosensitive polyimide.Alternatively, a light-blocking metal film can be used, which may beformed using chromium, molybdenum, nickel, titanium, cobalt, copper,tungsten, aluminum, or the like, for example.

There is no particular limitation on the formation method of thelight-blocking layer 414, and a dry method such as vapor deposition,sputtering, CVD, or the like or a wet method such as spin coating, dipcoating, spray coating, droplet discharging (e.g., ink jetting, screenprinting, or offset printing), or the like may be used depending on thematerial. If needed, an etching method (dry etching or wet etching) maybe employed to form a desired pattern.

The insulating layer 415 may be formed using an organic resin such asacrylic or polyimide by a coating method such as spin coating or variousprinting methods.

By formation of the light-blocking layer 414 on the counter substrateside in this manner, improvement in contrast and stabilization of thethin film transistor can be achieved. The light-blocking layer 414 canblock incident light on the semiconductor layer 403 of the thin filmtransistor 420; accordingly, electric characteristics of the thin filmtransistor 420 can be prevented from being varied due tophotosensitivity of the oxide semiconductor and can be stabilized.Further, the light-blocking layer 414 can prevent light leakage to anadjacent pixel, which allows higher contrast and higher definitiondisplay. Therefore, high definition and high reliability of the liquidcrystal display device can be achieved.

Improvement in contrast and viewing angle characteristics enables aliquid crystal display device with higher image quality to be supplied.Further, such a liquid crystal display device can be manufactured at lowcost with high productivity.

Further, characteristics of the thin film transistor can be stabilized;thus, reliability of the liquid crystal display device can be improved.

This embodiment can be implemented in combination with any of thestructures disclosed in other embodiments as appropriate.

Embodiment 5

A liquid crystal display device including a light-blocking layer (blackmatrix) is described with reference to FIGS. 6A and 6B.

As the film having a function of attenuating the intensity oftransmitting visible light, a coloring layer serving as a light-blockinglayer can be used. The liquid crystal display device illustrated inFIGS. 6A and 6B shows an example in which the light-blocking layer 414is formed in part of the interlayer film 413 on the first substrate 441(element substrate) side in the liquid crystal display deviceillustrated in FIGS. 1A and 1B of Embodiment 1. Therefore, components incommon with those in Embodiment 1 can be formed using a similar materialand a similar manufacturing method, and detailed description of the sameportions and portions having similar functions is omitted.

FIG. 6A is a plan view of a liquid crystal display device, and FIG. 6Bis a cross-sectional view along line X1 to X2 in FIG. 6A. Note that theplan view of FIG. 6A illustrates only the element substrate side and thecounter substrate side is not illustrated.

The interlayer film 413 includes the light-blocking layer 414 and thelight-transmitting chromatic-color resin layer 417. The light-blockinglayer 414 is provided on the first substrate 441 (element substrate)side and formed over the thin film transistor 420 (at least in a regionwhich covers the semiconductor layer of the thin film transistor) withthe insulating film 407 interposed therebetween, so that thelight-blocking layer 414 functions as a light-blocking layer whichshields the semiconductor layer 403 from light. On the other hand, thelight-transmitting chromatic-color resin layer 417 is formed in a regionwhich overlaps with the first electrode layer 447 and in a region whichoverlaps with the second electrode layer 446 and functions as a colorfilter layer. In the liquid crystal display device of FIG. 6B, part ofthe second electrode layer 446 is formed over the light-blocking layer414 and the liquid crystal layer 444 is provided thereover.

The light-blocking layer 414 has transmittance of visible light lowerthan the semiconductor layer 403 which is an oxide semiconductor layer.

Since the light-blocking layer 414 is used in the interlayer film, it ispreferable that black organic resin be used for the light-blocking layer414. For example, a black resin of a pigment material, carbon black,titanium black, or the like may be mixed into a resin material such asphotosensitive or non-photosensitive polyimide. As the formation methodof the light-blocking layer 414, a wet method such as spin coating, dipcoating, spray coating, droplet discharging (e.g., ink jetting, screenprinting, or offset printing), or the like or a dry method such as vapordeposition, sputtering, CVD, or the like may be used depending on thematerial. If needed, an etching method (dry etching or wet etching) maybe employed to form a desired pattern.

The light-blocking layer may be further formed on the counter substrateside of the liquid crystal display device because further improvement incontrast and stabilization of the thin film transistor can be achieved.When the light-blocking layer is formed on the counter substrate side,the light-blocking layer is formed in a region corresponding to the thinfilm transistor (at least in a region overlapping with the semiconductorlayer of the thin film transistor) with the liquid crystal layerinterposed therebetween, so that electric characteristics of the thinfilm transistor can be prevented from being varied due to light incidentfrom the counter substrate.

In the case of providing the light-blocking layer on the countersubstrate side, there is a case where light from the element substrateand light from the counter substrate toward the semiconductor layer ofthe thin film transistor can be blocked by a light-blocking wiringlayer, electrode layer, or the like. Thus, the light-blocking layer neednot always be formed to cover the thin film transistor.

Alternatively, the light-blocking layer may be provided so as to bestacked over or below the light-transmitting chromatic-color resinlayer. Examples of the stacked structure of the light-blocking layer andthe light-transmitting chromatic-color resin layer are illustrated inFIGS. 17A and 17B. In FIGS. 17A and 17B, an element layer 203 is formedover a first substrate 200 which is an element substrate and aninterlayer film 209 is formed over the element layer 203. The interlayerfilm 209 includes light-transmitting chromatic-color resin layers 204 a,204 b, and 204 c and light-blocking layers 205 a, 205 b, 205 c, and 205d. The light-blocking layers 205 a, 205 b, 205 c, and 205 d are formedat boundaries of the light-transmitting chromatic-color resin layers 204a, 204 b, and 204 c. Note that the pixel electrode layer and the commonelectrode layer are omitted in FIGS. 17A and 17B.

A plurality of chromatic colors can be used. For example, the liquidcrystal display device in FIGS. 17A and 17B may use a coloring layer ofred, a coloring layer of green, and a coloring layer of blue as thelight-transmitting chromatic-color resin layer 204 a, thelight-transmitting chromatic-color resin layer 204 b, and thelight-transmitting chromatic-color resin layer 204 c, respectively;thus, light-transmitting chromatic-color resin layers of plural colorsare used.

FIGS. 17A and 17B illustrate examples in which thin films that arethinner than the light-transmitting chromatic-color resin layers areused as the light-blocking layers and the light-blocking layers arestacked below or over the light-transmitting chromatic-color resinlayers. As such light-blocking layers, thin films of light-blockinginorganic films (e.g., metal films) are preferable.

In FIG. 17A, thin films of the light-blocking layers 205 a, 205 b, 205c, and 205 d are formed over the element layer 203, and thelight-transmitting chromatic-color resin layers 204 a, 204 b, and 204 care stacked over the light-blocking layers 205 a, 205 b, 205 c, and 205d. In FIG. 17B, the light-transmitting chromatic-color resin layers 204a, 204 b, and 204 c are formed over the element layer 203; thin films ofthe light-blocking layers 205 a, 205 b, 205 c, and 205 d are stackedover the light-transmitting chromatic-color resin layers 204 a, 204 b,and 204 c; and an insulating film 211 is formed as an overcoat film overthe light-blocking layers 205 a, 205 b, 205 c, and 205 d. The elementlayer, the light-blocking layers, and the light-transmittingchromatic-color resin layers may be stacked directly as illustrated inFIG. 17B, or they may have an insulating film over, below, or betweenthe layers.

As sealants 202 a and 202 b, it is typically preferable to use a visiblelight curable resin, an ultraviolet curable resin, or a thermosettingresin. Typically, an acrylic resin, an epoxy resin, an amine resin, orthe like can be used. Further, a photopolymerization initiator(typically, an ultraviolet light polymerization initiator), athermosetting agent, a filler, or a coupling agent may be included inthe sealants 202 a and 202 b.

When the light-blocking layer is provided in this manner, thelight-blocking layer can block incident light on the semiconductor layer403 of the thin film transistor without reduction in an aperture ratioof a pixel; accordingly, electric characteristics of the thin filmtransistor can be prevented from being varied due to photosensitivity ofthe oxide semiconductor and can be stabilized. Further, thelight-blocking layer can prevent light leakage to an adjacent pixel,which enables higher contrast and higher definition display. Therefore,high definition and high reliability of the liquid crystal displaydevice can be achieved.

Further, the light-transmitting chromatic-color resin layer 417 canfunction as a color filter layer. In the case of providing the colorfilter layer on the counter substrate side, precise positional alignmentof a pixel region with an element substrate over which the thin filmtransistor is formed is difficult, and accordingly there is apossibility that image quality is degraded. Here, since thelight-transmitting chromatic-color resin layer 417 is formed directly onthe element substrate side, the formation region can be controlled moreprecisely and this structure is adjustable to a pixel with a finepattern. In addition, one insulating layer can serve as both theinterlayer film and the color filter layer, whereby the process can besimplified and a liquid crystal display device can be manufactured atlow cost.

Improvement in contrast and viewing angle characteristics enables aliquid crystal display device with higher image quality to be supplied.Further, such a liquid crystal display device can be manufactured at lowcost with high productivity.

Further, characteristics of the thin film transistor can be stabilized;thus, reliability of the liquid crystal display device can be improved.

This embodiment can be implemented in combination with any of thestructures disclosed in other embodiments as appropriate.

Embodiment 6

Another example of a thin film transistor which can be applied to theliquid crystal display devices in Embodiments 1 to 5 is described. Notethat components in common with those in Embodiments 1 to 5 can be formedusing a similar material and a similar manufacturing method, anddetailed description of the same portions and portions having similarfunctions is omitted.

An example of a liquid crystal display device including a thin filmtransistor which has a structure in which source and drain electrodelayers are in contact with a semiconductor layer without an n⁺ layerinterposed therebetween is illustrated in FIGS. 10A and 10B.

FIG. 10A is a plan view of a liquid crystal display device andillustrates one pixel. FIG. 10B is a cross-sectional view along line V1to V2 in FIG. 10A.

In the plane view of FIG. 10A, in a manner similar to Embodiment 1, aplurality of source wiring layers (including the wiring layer 405 a) areprovided in parallel to each other (extended in a vertical direction inthe drawing) and apart from each other. A plurality of gate wiringlayers (including the gate electrode layer 401) are provided apart fromeach other and extended in a direction generally perpendicular to thesource wiring layers (a horizontal direction in the drawing). Commonwiring layers (common electrode layers) are provided adjacent to therespective plurality of gate wiring layers and extended in a directiongenerally parallel to the gate wiring layers, that is, in a directiongenerally perpendicular to the source wiring layers (a horizontaldirection in the drawing). A roughly rectangular space is surrounded bythe source wiring layers, the common wiring layers (common electrodelayers), and the gate wiring layers. In this space, a pixel electrodelayer and a common electrode layer of the liquid crystal display deviceare provided. A thin film transistor 422 for driving the pixel electrodelayer is provided at the upper left corner in the drawing. A pluralityof pixel electrode layers and thin film transistors are provided inmatrix.

In the liquid crystal display device of FIGS. 10A and 10B, the secondelectrode layer 446 electrically connected to the thin film transistor422 functions as a pixel electrode layer, and the first electrode layer447 electrically connected to the common wiring layer functions as acommon electrode layer. Note that as shown in FIGS. 10A and 10B, thefirst electrode layer 447 also serves as the common wiring layer in thepixel; thus, adjacent pixels are electrically connected to each otherwith the common electrode layer 409. Note than a capacitor is formedwith the pixel electrode layer and the common electrode layer.

The first substrate 441 provided with the thin film transistor 422, theinterlayer film 413 which is a light-transmitting chromatic-color resinlayer, the first electrode layer 447, and the second electrode layer 446and the second substrate 442 are firmly attached to each other with theliquid crystal layer 444 interposed therebetween.

The thin film transistor 422 has a structure in which the semiconductorlayer 403 is in contact with the wiring layers 405 a and 405 b servingas source and drain electrode layers without an n⁺ layer interposedtherebetween.

When a coloring layer which is the light-transmitting chromatic-colorresin layer 417 is used as the interlayer film 413 provided over thethin film transistor 422, the intensity of incident light on thesemiconductor layer 403 of the thin film transistor 422 can beattenuated without reduction in an aperture ratio of a pixel.Accordingly, electric characteristics of the thin film transistor 422can be prevented from being varied due to photosensitivity of the oxidesemiconductor and can be stabilized. Further, the light-transmittingchromatic-color resin layer 417 can function as a color filter layer. Inthe case of providing the color filter layer on the counter substrateside, precise positional alignment of a pixel region with an elementsubstrate over which the thin film transistor is formed is difficult,and accordingly there is a possibility that image quality is degraded.Here, since the interlayer film is formed as the color filter layerdirectly on the element substrate side, the formation region can becontrolled more precisely and this structure is adjustable to a pixelwith a fine pattern. In addition, one insulating layer can serve as boththe interlayer film and the color filter layer, whereby the process canbe simplified and a liquid crystal display device can be manufactured atlow cost.

Improvement in contrast and viewing angle characteristics and higherresponse speed enable a liquid crystal display device with higher imagequality and higher performance to be supplied. Further, such a liquidcrystal display device can be manufactured at low cost with highproductivity.

Further, characteristics of the thin film transistor can be stabilized;thus, reliability of the liquid crystal display device can be improved.

This embodiment can be implemented in combination with any of thestructures disclosed in other embodiments as appropriate.

Embodiment 7

Another example of a thin film transistor which can be applied to theliquid crystal display devices in Embodiments 1 to 5 are described withreference to FIGS. 9A and 9B.

FIG. 9A is a plan view of a liquid crystal display device andillustrates one pixel. FIG. 9B is a cross-sectional view along line Z1to Z2 in FIG. 9A.

In the plane view of FIG. 9A, in a manner similar to Embodiment 1, aplurality of source wiring layers (including the wiring layer 405 a) areprovided in parallel to each other (extended in a vertical direction inthe drawing) and apart from each other. A plurality of gate wiringlayers (including the gate electrode layer 401) are provided apart fromeach other and extended in a direction generally perpendicular to thesource wiring layers (a horizontal direction in the drawing). Commonwiring layers (common electrode layers) are provided adjacent to therespective plurality of gate wiring layers and extended in a directiongenerally parallel to the gate wiring layers, that is, in a directiongenerally perpendicular to the source wiring layers (a horizontaldirection in the drawing). A roughly rectangular space is surrounded bythe source wiring layers, the common wiring layers (common electrodelayers), and the gate wiring layers. In this space, a pixel electrodelayer and a common electrode layer of the liquid crystal display deviceare provided. A thin film transistor 421 for driving the pixel electrodelayer is provided at the upper left corner in the drawing. A pluralityof pixel electrode layers and thin film transistors are provided inmatrix.

In the liquid crystal display device of FIGS. 9A and 9B, the secondelectrode layer 446 electrically connected to the thin film transistor421 functions as a pixel electrode layer, and the first electrode layer447 electrically connected to the common wiring layer functions as acommon electrode layer. Note that, as shown in FIGS. 9A and 9B, thefirst electrode layer 447 also serves as the common wiring layer in thepixel; thus, adjacent pixels are electrically connected to each otherwith the common electrode layer 409. Note that a capacitor is formedwith the pixel electrode layer and the common electrode layer.

The first substrate 441 provided with the thin film transistor 421, theinterlayer film 413 which is a light-transmitting chromatic-color resinlayer, the first electrode layer 447, and a second electrode layer 446and the second substrate 442 are firmly attached to each other with theliquid crystal layer 444 interposed therebetween.

The thin film transistor 421 is a bottom-gate thin film transistor andincludes, over the first substrate 441 having an insulating surface, thegate electrode layer 401, the gate insulating layer 402, the wiringlayers 405 a and 405 b serving as source and drain electrode layers, then⁺ layers 404 a and 404 b serving as source and drain regions, and thesemiconductor layer 403. In addition, the insulating film 407 whichcovers the thin film transistor 421 and is in contact with thesemiconductor layer 403 is provided. An In—Ga—Zn—O-basednon-single-crystal film is used for the semiconductor layer 403 and then⁺ layers 404 a and 404 b. The thin film transistor 421 having such astructure shows characteristics of a mobility of 20 cm²/Vs or more and asubthreshold swing (S value) of 0.4 V/dec or less. Thus, the thin filmtransistor can operate at high speed, and a driver circuit (a sourcedriver or a gate driver) such as a shift register can be formed over thesame substrate as the pixel portion is.

It is preferable that reverse sputtering in which an argon gas isintroduced to generate plasma be performed on the gate insulating layer402 and the wiring layers 405 a and 405 b before formation of thesemiconductor layer 403 by sputtering, in order to remove dust attachedto surfaces.

The semiconductor layer 403 and the n⁺ layers 404 a and 404 b arepreferably subjected to heat treatment at 200° C. to 600° C., typically300° C. to 500° C. For example, heat treatment is performed for 1 hourat 350° C. in a nitrogen atmosphere. There is no particular limitationon when to perform this heat treatment, as long as it is performed afteroxide semiconductor films used for the semiconductor layer 403 and then⁺ layers 404 a and 404 b are formed.

In addition, oxygen radical treatment may be performed on thesemiconductor layer 403.

The gate insulating layer 402 exists in the entire region including thethin film transistor 421, and the thin film transistor 421 is providedwith the gate electrode layer 401 between the gate insulating layer 402and the first substrate 441 which is a substrate having an insulatingsurface. The wiring layers 405 a and 405 b and the n⁺ layers 404 a and404 b are provided over the gate insulating layer 402. In addition, thesemiconductor layer 403 is provided over the gate insulating layer 402,the wiring layers 405 a and 405 b, and the n⁺ layers 404 a and 404 b.Although not illustrated, a wiring layer is provided over the gateinsulating layer 402 in addition to the wiring layers 405 a and 405 band the wiring layer extends beyond the perimeter of the semiconductorlayer 403 to the outside.

When a coloring layer which is the light-transmitting chromatic-colorresin layer 417 is used as the interlayer film 413 provided over thethin film transistor 421, the intensity of incident light on thesemiconductor layer 403 of the thin film transistor 421 can beattenuated without reduction in an aperture ratio of a pixel.Accordingly, electric characteristics of the thin film transistor 421can be prevented from being varied due to photosensitivity of the oxidesemiconductor and can be stabilized. Further, the light-transmittingchromatic-color resin layer 417 can function as a color filter layer. Inthe case of providing the color filter layer on the counter substrateside, precise positional alignment of a pixel region with an elementsubstrate over which the thin film transistor is formed is difficult,and accordingly there is a possibility that image quality is degraded.Here, since the interlayer film is formed as the color filter layerdirectly on the element substrate side, the formation region can becontrolled more precisely and this structure is adjustable to a pixelwith a fine pattern. In addition, one insulating layer can serve as boththe interlayer film and the color filter layer, whereby the process canbe simplified and a liquid crystal display device can be manufactured atlow cost.

Improvement in contrast and viewing angle characteristics enables aliquid crystal display device with higher image quality to be supplied.Further, such a liquid crystal display device can be manufactured at lowcost with high productivity.

Further, characteristics of the thin film transistor can be stabilized;thus, reliability of the liquid crystal display device can be improved.

This embodiment can be implemented in combination with any of thestructures disclosed in other embodiments as appropriate.

Embodiment 8

Another example of a thin film transistor which can be applied to theliquid crystal display devices in Embodiments 1 to 5 is described. Notethat components in common with those in Embodiments 1 to 5 can be formedusing a similar material and a similar manufacturing method, anddetailed description of the same portions and portions having similarfunctions is omitted.

An example of a liquid crystal display device including a thin filmtransistor which has a structure in which source and drain electrodelayers are in contact with a semiconductor layer without an n⁺ layerinterposed therebetween is illustrated in FIGS. 11A and 11B.

FIG. 11A is a plan view of a liquid crystal display device andillustrates one pixel. FIG. 11B is a cross-sectional view along line Y1to Y2 in FIG. 11A.

In the plan view of FIG. 11A, in a manner similar to Embodiment 1, aplurality of source wiring layers (including the wiring layer 405 a) areprovided in parallel to each other (extended in a vertical direction inthe drawing) and apart from each other. A plurality of gate wiringlayers (including the gate electrode layer 401) are provided apart fromeach other and extended in a direction generally perpendicular to thesource wiring layers (a horizontal direction in the drawing). Commonwiring layers (common electrode layers) are provided adjacent to therespective plurality of gate wiring layers and extended in a directiongenerally parallel to the gate wiring layers, that is, in a directiongenerally perpendicular to the source wiring layers (a horizontaldirection in the drawing). A roughly rectangular space is surrounded bythe source wiring layers, the common electrode layers (common electrodelayers), and the gate wiring layers. In this space, a pixel electrodelayer and a common electrode layer of the liquid crystal display deviceare provided. A thin film transistor 423 for driving the pixel electrodelayer is provided at the upper left corner in the drawing. A pluralityof pixel electrode layers and thin film transistors are provided inmatrix.

In the liquid crystal display device of FIGS. 11A and 11B, the secondelectrode layer 446 electrically connected to the thin film transistor432 functions as a pixel electrode layer, and the first electrode layer447 electrically connected to the common wiring layer functions as acommon electrode layer. Note that as shown in FIGS. 11A and 11B, thefirst electrode layer 447 also serves as the common wiring layer in thepixel; thus adjacent pixels are electrically connected to each otherwith the common electrode layer 409. Note that a capacitor is formedwith the pixel electrode layer and the common electrode layer.

The first substrate 441 provided with the thin film transistor 423, theinterlayer film 413 which is a light-transmitting chromatic-color resinlayer, the first electrode layer 447, and the second electrode layer 446and the second substrate 442 are firmly attached to each other with theliquid crystal layer 444 interposed therebetween.

The gate insulating layer 402 exists in the entire region including thethin film transistor 423, and the thin film transistor 423 is providedwith the gate electrode layer 401 between the gate insulating layer 402and the first substrate 441 which is a substrate having an insulatingsurface. The wiring layers 405 a and 405 b are provided over the gateinsulating layer 402. In addition, the semiconductor layer 403 isprovided over the gate insulating layer 402 and the wiring layers 405 aand 405 b. Although not illustrated, a wiring layer is provided over thegate insulating layer 402 in addition to the wiring layers 405 a and 405b, and the wiring layer extends beyond the perimeter of thesemiconductor layer 403 to the outside.

When a coloring layer which is the light-transmitting chromatic-colorresin layer 417 is used as the interlayer film 413 provided over thethin film transistor 423, the intensity of incident light on thesemiconductor layer 403 of the thin film transistor 423 can beattenuated without reduction in an aperture ratio of a pixel.Accordingly, electric characteristics of the thin film transistor 423can be prevented from being varied due to photosensitivity of the oxidesemiconductor and can be stabilized. Further, the light-transmittingchromatic-color resin layer 417 can function as a color filter layer. Inthe case of providing the color filter layer on the counter substrateside, precise positional alignment of a pixel region with an elementsubstrate over which the thin film transistor is formed is difficult,and accordingly there is a possibility that image quality is degraded.Here, since the interlayer film is formed as the color filter layerdirectly on the element substrate side, the formation region can becontrolled more precisely and this structure is adjustable to a pixelwith a fine pattern. In addition, one insulating layer can serve as boththe interlayer film and the color filter layer, whereby the process canbe simplified and a liquid crystal display device can be manufactured atlow cost.

Improvement in contrast and viewing angle characteristics enables aliquid crystal display device with higher image quality to be supplied.Further, such a liquid crystal display device can be manufactured at lowcost with high productivity.

Further, characteristics of the thin film transistor can be stabilized;thus, reliability of the liquid crystal display device can be improved.

This embodiment can be implemented in combination with any of thestructures disclosed in other embodiments as appropriate.

Embodiment 9

A liquid crystal material which exhibits a blue phase can be used forthe liquid crystal layer in the above-described Embodiments. A liquidcrystal display device which uses a liquid crystal layer exhibiting ablue phase is described with reference to FIGS. 2A to 2D.

FIGS. 2A to 2D are cross-sectional views of a liquid crystal displaydevice and its manufacturing process.

In FIG. 2A, the element layer 203 is formed over the first substrate 200which is an element substrate, and the interlayer film 209 is formedover the element layer 203.

The interlayer film 209 includes the light-transmitting chromatic-colorresin layers 204 a, 204 b, and 204 c and the light-blocking layers 205a, 205 b, 205 c, and 205 d which are alternately arranged such that thelight-blocking layers sandwich the light-transmitting chromatic-colorresin layers. Note that the pixel electrode layer and the commonelectrode layer are omitted in FIGS. 2A to 2D. For example, the pixelelectrode layer and the common electrode layer can have any of thestructures described in Embodiments 1 to 8, and a lateral electric fieldmode can be employed.

As illustrated in FIG. 2B, the first substrate 200 and the secondsubstrate 201 which is a counter substrate are firmly fixed with thesealants 202 a and 202 b with a liquid crystal layer 206 interposedtherebetween. As a method for forming the liquid crystal layer 206, adispenser method (dripping method) or an injection method in which afterattachment of the first substrate 200 and the second substrate 201,liquid crystal is injected with the use of capillary phenomenon can beused.

A liquid crystal material exhibiting a blue phase can be used for theliquid crystal layer 206. The liquid crystal material exhibiting a bluephase has a short response time of 1 msec or less and enables high-speedresponse, whereby the liquid crystal display device can show highperformance.

The liquid crystal material exhibiting a blue phase includes a liquidcrystal and a chiral agent. The chiral agent is employed to align theliquid crystal in a helical structure and to make the liquid crystalexhibit a blue phase. For example, a liquid crystal material into whicha chiral agent is mixed at 5 wt % or more may be used for the liquidcrystal layer.

As the liquid crystal, a thermotropic liquid crystal, a low-molecularliquid crystal, a high-molecular liquid crystal, a ferroelectric liquidcrystal, an anti-ferroelectric liquid crystal, or the like is used.

As the chiral agent, a material having a high compatibility with aliquid crystal and a strong twisting power is used. Either one of twoenantiomers, R and S, is used, and a racemic mixture in which R and Sare mixed at 50:50 is not used.

The above liquid crystal material exhibits a cholesteric phase, acholesteric blue phase, a smectic phase, a smectic blue phase, a cubicphase, a chiral nematic phase, an isotropic phase, or the like dependingon conditions.

A cholesteric blue phase and a smectic blue phase, which are bluephases, are seen in a liquid crystal material having a cholesteric phaseor a smectic phase with a relatively short helical pitch of less than orequal to 500 nm. The alignment of the liquid crystal material has adouble twist structure. Having the order of less than or equal to anoptical wavelength, the liquid crystal material is transparent, andoptical modulation action is generated through a change in alignmentorder by voltage application. A blue phase is optically isotropic andthus has no viewing angle dependence. Thus, an alignment film is notnecessarily formed; therefore, display image quality can be improved andcost can be reduced. In addition, rubbing treatment on an alignment filmis unnecessary; accordingly, electrostatic discharge damage caused bythe rubbing treatment can be prevented and defects and damage of theliquid crystal display device in the manufacturing process can bereduced. Thus, productivity of the liquid crystal display device can beincreased. A thin film transistor that uses an oxide semiconductor layerparticularly has a possibility that electric characteristics of the thinfilm transistor may fluctuate significantly by the influence of staticelectricity and deviate from the designed range. Therefore, it is moreeffective to use a blue phase liquid crystal material for a liquidcrystal display device including a thin film transistor that uses anoxide semiconductor layer.

The blue phase appears only within a narrow temperature range;therefore, it is preferable that a photocurable resin and aphotopolymerization initiator be added to a liquid crystal material andpolymer stabilization treatment be performed in order to widen thetemperature range. The polymer stabilization treatment is performed insuch a manner that a liquid crystal material including a liquid crystal,a chiral agent, a photocurable resin, and a photopolymerizationinitiator is irradiated with light having a wavelength with which thephotocurable resin and the photopolymerization initiator are reacted.This polymer stabilization treatment may be performed by irradiating aliquid crystal material exhibiting an isotropic phase with light or byirradiating a liquid crystal material exhibiting a blue phase under thecontrol of the temperature with light. For example, the polymerstabilization treatment is performed in the following manner: thetemperature of a liquid crystal layer is controlled and under the statein which the blue phase is exhibited, the liquid crystal layer isirradiated with light. However, the polymer stabilization treatment isnot limited to this manner and may be performed in such a manner that aliquid crystal layer under the state of exhibiting an isotropic phase ata temperature within +10° C., preferably +5° C. of the phase transitiontemperature between the blue phase and the isotropic phase is irradiatedwith light. The phase transition temperature between the blue phase andthe isotropic phase is a temperature at which the phase changes from theblue phase to the isotropic phase when the temperature rises, or atemperature at which the phase changes from the isotropic phase to theblue phase when the temperature decreases. As an example of the polymerstabilization treatment, the following method can be employed: afterheating a liquid crystal layer to exhibit the isotropic phase, thetemperature of the liquid crystal layer is gradually decreased so thatthe phase changes to the blue phase, and then, irradiation with light isperformed while the temperature at which the blue phase is exhibited iskept. Alternatively, after the phase changes to the isotropic phase bygradually heating a liquid crystal layer, the liquid crystal layer canbe irradiated with light under a temperature within +10° C., preferably+5° C. of the phase transition temperature between the blue phase andthe isotropic phase (under the state of exhibiting an isotropic phase).In the case of using an ultraviolet curable resin (a UV curable resin)as the photocurable resin included in the liquid crystal material, theliquid crystal layer may be irradiated with ultraviolet rays. Even inthe case where the blue phase is not exhibited, if polymer stabilizationtreatment is performed by irradiation with light under a temperaturewithin +10° C., preferably +5° C. of the phase transition temperaturebetween the blue phase and the isotropic phase (under the state ofexhibiting an isotropic phase), the response time can be made as shortas 1 msec or less and high-speed response is possible.

The photocurable resin may be a monofunctional monomer such as acrylateor methacrylate; a polyfunctional monomer such as diacrylate,triacrylate, dimethacrylate, or trimethacrylate; or a mixture thereof.Further, the photocurable resin may have liquid crystallinity,non-liquid crystallinity, or both of them. A resin which is cured withlight having a wavelength with which the photopolymerization initiatorto be used is reacted may be selected as the photocurable resin, and anultraviolet curable resin can be typically used.

As the photopolymerization initiator, a radical polymerization initiatorwhich generates radicals by light irradiation, an acid generator whichgenerates an acid by light irradiation, or a base generator whichgenerates a base by light irradiation may be used.

Specifically, a mixture of JC-1041XX (produced by Chisso Corporation)and 4-cyano-4′-pentylbiphenyl can be used as the liquid crystalmaterial. ZLI-4572 (produced by Merck Ltd., Japan) can be used as thechiral agent. As the photocurable resin, 2-ethylhexyl acrylate, RM257(produced by Merck Ltd., Japan), or trimethylolpropane triacrylate canbe used. As the photopolymerization initiator,2,2-dimethoxy-2-phenylacetophenone can be used.

The liquid crystal layer 206 is formed using a liquid crystal materialincluding a liquid crystal, a chiral agent, a photocurable resin, and aphotopolymerization initiator.

As illustrated in FIG. 2C, polymer stabilization treatment is performedon the liquid crystal layer 206 by irradiation with light 207, so that aliquid crystal layer 208 is formed. The light 207 is light having awavelength with which the photocurable resin and the photopolymerizationinitiator included in the liquid crystal layer 206 are reacted. By thispolymer stabilization treatment using light irradiation, the temperaturerange in which the liquid crystal layer 208 exhibits a blue phase can bewidened.

In the case where a photocurable resin such as an ultraviolet curableresin is used as a sealant and a liquid crystal layer is formed by adropping method, for example, the sealant may be cured by the lightirradiation step of the polymer stabilization treatment.

When a liquid crystal display device has a structure in which a colorfilter layer and a light-blocking layer are formed over an elementsubstrate as illustrated in FIGS. 2A to 2D, irradiation light from thecounter substrate side is not absorbed or blocked by the color filterlayer and the light-blocking layer; accordingly, the entire region ofthe liquid crystal layer can be uniformly irradiated with the light.Thus, alignment disorder of a liquid crystal due to nonuniformphotopolymerization, display unevenness due to the alignment disorder,and the like can be prevented. In addition, since a thin film transistoris shielded from light by the light-blocking layer, electriccharacteristics of the thin film transistor are kept stable.

As illustrated in FIG. 2D, a polarizing plate 210 a is provided on theouter side (a side opposite from a side provided with the liquid crystallayer 208) of the first substrate 200 and a polarizing plate 210 b isprovided on the outer side (a side opposite from a side provided withthe liquid crystal layer 208) of the second substrate 201. In additionto the polarizing plates, an optical film such as a retardation plate oran anti-reflection film may be provided. For example, circularpolarization may be employed using a polarizing plate or a retardationplate. Through the above-described process, a liquid crystal displaydevice can be completed.

In the case of manufacturing a plurality of liquid crystal displaydevices using a large-sized substrate (a so-called multiple panelmethod), a division step can be performed before the polymerstabilization treatment or before provision of the polarizing plates. Inconsideration of the influence of the division step on the liquidcrystal layer (such as alignment disorder due to force applied in thedivision step), it is preferable that the division step be performedafter the attachment between the first substrate and the secondsubstrate and before the polymer stabilization treatment.

Although not illustrated, a backlight, a sidelight, or the like may beused as a light source. Light from the light source is emitted from theside of the first substrate 200, which is an element substrate, so as topass through the second substrate 201 on the viewer side.

Improvement in contrast and viewing angle characteristics enables aliquid crystal display device with higher image quality and higherperformance to be supplied. Further, such a liquid crystal displaydevice can be manufactured at low cost with high productivity.

Further, characteristics of the thin film transistor can be stabilized;thus, reliability of the liquid crystal display device can be improved.

This embodiment can be implemented in combination with any of thestructures disclosed in other embodiments as appropriate.

Embodiment 10

A thin film transistor is manufactured, and a liquid crystal displaydevice having a display function can be manufactured using the thin filmtransistor in a pixel portion and further in a driver circuit. Further,part or whole of a driver circuit can be formed over the same substrateas a pixel portion is, using a thin film transistor, whereby asystem-on-panel can be obtained.

The liquid crystal display device includes a liquid crystal element(also referred to as a liquid crystal display element) as a displayelement.

Further, a liquid crystal display device includes a panel in which aliquid crystal display element is sealed, and a module in which an IC orthe like including a controller is mounted to the panel. An embodimentof the present invention also relates to an element substrate, whichcorresponds to one mode before the display element is completed in amanufacturing process of the liquid crystal display device, and theelement substrate is provided with means for supplying current to thedisplay element in each of a plurality of pixels. Specifically, theelement substrate may be in a state after only a pixel electrode of thedisplay element is formed, a state after a conductive film to be a pixelelectrode is formed and before the conductive film is etched to form thepixel electrode, or any of other states.

Note that a liquid crystal display device in this specification means animage display device, a display device, or a light source (including alighting device). Furthermore, the liquid crystal display device alsoincludes the following modules in its category: a module to which aconnector such as a flexible printed circuit (FPC), a tape automatedbonding (TAB) tape, or a tape carrier package (TCP) is attached; amodule having a TAB tape or a TCP at the tip of which a printed wiringboard is provided; and a module in which an integrated circuit (IC) isdirectly mounted on a display element by chip on glass (COG).

The appearance and a cross section of a liquid crystal display panel,which is one embodiment of a liquid crystal display device, is describedwith reference to FIGS. 12A to 12C. FIGS. 12A and 12 B are top views ofa panel in which highly reliable thin film transistors 4010 and 4011each including an oxide semiconductor film as a semiconductor layer anda liquid crystal element 4013 are sealed between a first substrate 4001and a second substrate 4006 with a sealant 4005. FIG. 12C is across-sectional view along line M to N of FIGS. 12A and 12B.

The sealant 4005 is provided so as to surround a pixel portion 4002 anda scanning line driver circuit 4004 that are provided over the firstsubstrate 4001. The second substrate 4006 is provided over the pixelportion 4002 and the scanning line driver circuit 4004. Therefore, thepixel portion 4002 and the scanning line driver circuit 4004 are sealedtogether with a liquid crystal layer 4008, by the first substrate 4001,the sealant 4005, and the second substrate 4006.

In FIG. 12A, a signal line driver circuit 4003 that is formed using asingle crystal semiconductor film or a polycrystalline semiconductorfilm over a substrate separately prepared is mounted in a region that isdifferent from the region surrounded by the sealant 4005 over the firstsubstrate 4001. In contrast, FIG. 12B illustrates an example in whichpart of a signal line driver circuit is formed over the first substrate4001 with use of a thin film transistor including an oxidesemiconductor. A signal line driver circuit 4003 b is formed over thefirst substrate 4001 and a signal line driver circuit 4003 a which isformed using a single crystal semiconductor film or a polycrystallinesemiconductor film is mounted on the substrate separately prepared.

Note that there is no particular limitation on the connection method ofa driver circuit which is separately formed, and a COG method, a wirebonding method, a TAB method, or the like can be used. FIG. 12Aillustrates an example of mounting the signal line driver circuit 4003by a COG method, and FIG. 12B illustrates an example of mounting thesignal line driver circuit 4003 by a TAB method.

The pixel portion 4002 and the scanning line driver circuit 4004provided over the first substrate 4001 include a plurality of thin filmtransistors. FIG. 12C illustrates the thin film transistor 4010 includedin the pixel portion 4002 and the thin film transistor 4011 included inthe scanning line driver circuit 4004. An insulating layer 4020 and aninterlayer film 4021 are provided over the thin film transistors 4010and 4011.

Any of the highly reliable thin film transistors including an oxidesemiconductor film as a semiconductor layer, which are described inEmbodiments 1 to 8, can be used as the thin film transistors 4010 and4011. The thin film transistors 4010 and 4011 are n-channel thin filmtransistors.

A pixel electrode layer 4030 and a common electrode layer 4031 areprovided over the first substrate 4001, and the pixel electrode layer4030 is electrically connected to the thin film transistor 4010. Theliquid crystal element 4013 includes the pixel electrode layer 4030, thecommon electrode layer 4031, and the liquid crystal layer 4008. Notethat a polarizing plate 4032 and a polarizing plate 4033 are provided onthe outer sides of the first substrate 4001 and the second substrate4006, respectively.

As the first substrate 4001 and the second substrate 4006, glass,plastic, or the like having a light-transmitting property can be used.As plastic, a fiberglass-reinforced plastics (FRP) plate, a polyvinylfluoride (PVF) film, a polyester film, or an acrylic resin film can beused. Further, sheet in which aluminum foil is sandwiched by PVF filmsor polyester films can also be used.

A columnar spacer denoted by reference numeral 4035 is obtained byselective etching of an insulating film and is provided in order tocontrol the thickness (a cell gap) of the liquid crystal layer 4008.Note that a spherical spacer may be used. In the liquid crystal displaydevice using the liquid crystal layer 4008, the thickness (the cell gap)of the liquid crystal layer 4008 is preferably about 5 μm to 20 μm.

Although FIGS. 12A to 12C illustrate examples of transmissive liquidcrystal display devices, an embodiment of the present invention can alsobe applied to a transflective liquid crystal display device.

FIGS. 12A to 12C illustrate examples of liquid crystal display devicesin which a polarizing plate is provided on the outer side (the viewside) of a substrate; however, the polarizing plate may be provided onthe inner side of the substrate. The position of the polarizing platemay be determined as appropriate depending on the material of thepolarizing plate and conditions of the manufacturing process.Furthermore, a light-blocking layer serving as a black matrix may beprovided.

The interlayer film 4021 is a light-transmitting chromatic-color resinlayer and functions as a color filter layer. A light-blocking layer maybe included in part of the interlayer film 4021. In FIGS. 12A to 12C, alight-blocking layer 4034 is provided on the second substrate 4006 sideso as to cover the thin film transistors 4010 and 4011. By thelight-blocking layer 4034, improvement in contrast and stabilization ofthe thin film transistors can be achieved.

When a coloring layer which is the light-transmitting chromatic-colorresin layer is used as the interlayer film 4021 provided over the thinfilm transistor, the intensity of incident light on the semiconductorlayer of the thin film transistor can be attenuated without reduction inan aperture ratio of a pixel. Accordingly, electric characteristics ofthe thin film transistor can be prevented from being varied due tophotosensitivity of the oxide semiconductor and can be stabilized.Further, the light-transmitting chromatic-color resin layer can functionas a color filter layer. In the case of providing the color filter layeron the counter substrate side, precise positional alignment of a pixelregion with an element substrate over which the thin film transistor isformed is difficult, and accordingly there is a possibility that imagequality is degraded. Here, since the interlayer film is formed as thecolor filter layer directly on the element substrate side, the formationregion can be controlled more precisely and this structure is adjustableto a pixel with a fine pattern. In addition, one insulating layer canserve as both the interlayer film and the color filter layer, wherebythe process can be simplified and a liquid crystal display device can bemanufactured at low cost.

The thin film transistors may be covered with the insulating layer 4020which serves as a protective film of the thin film transistors; however,there is no particular limitation to such a structure.

Note that the protective film is provided to prevent entry of impuritiesfloating in air, such as an organic substance, a metal substance, ormoisture, and is preferably a dense film. The protective film may beformed by a sputtering method to be a single-layer film or a stack of asilicon oxide film, a silicon nitride film, a silicon oxynitride film, asilicon nitride oxide film, an aluminum oxide film, an aluminum nitridefilm, an aluminum oxynitride film, and/or an aluminum nitride oxidefilm.

After the protective film is formed, the semiconductor layer may besubjected to annealing (300° C. to 400° C.).

Further, in the case of further forming a light-transmitting insulatinglayer as a planarizing insulating film, the light-transmittinginsulating layer can be formed using an organic material having heatresistance, such as polyimide, acrylic, benzocyclobutene, polyamide, orepoxy. Other than such organic materials, it is also possible to use alow-dielectric constant material (a low-k material), a siloxane-basedresin, PSG (phosphosilicate glass), BPSG (borophosphosilicate glass), orthe like. The insulating layer may be formed by stacking a plurality ofinsulating films formed of these materials.

There is no particular limitation on the formation method of theinsulating layer having a stacked structure, and the following methodcan be employed in accordance with the material: sputtering, an SOGmethod, spin coating, dip coating, spray coating, droplet discharging(e.g., ink jetting, screen printing, or offset printing), doctor knife,roll coating, curtain coating, knife coating, or the like. In the casewhere the insulating layer is formed using a material solution, thesemiconductor layer may be annealed (at 200° C. to 400° C.) at the sametime of a baking step. The baking step of the insulating layer alsoserves as the annealing step of the semiconductor layer, whereby aliquid crystal display device can be manufactured efficiently.

The pixel electrode layer 4030 and the common electrode layer 4031 canbe formed using a light-transmitting conductive material such as indiumoxide containing tungsten oxide, indium zinc oxide containing tungstenoxide, indium oxide containing titanium oxide, indium tin oxidecontaining titanium oxide, indium tin oxide (hereinafter referred to asITO), indium zinc oxide, or indium tin oxide to which silicon oxide isadded.

A conductive composition containing a conductive high molecule (alsoreferred to as a conductive polymer) can be used for the pixel electrodelayer 4030 and the common electrode layer 4031.

In addition, a variety of signals and potentials are supplied to thesignal line driver circuit 4003 which is formed separately, and thescanning line driver circuit 4004 or the pixel portion 4002 from an FPC4018.

Further, since the thin film transistor is easily broken by staticelectricity and the like, a protection circuit for protecting the drivercircuits is preferably provided over the same substrate for a gate lineor a source line. The protection circuit is preferably formed using anonlinear element in which an oxide semiconductor is used.

In FIGS. 12A to 12C, a connecting terminal electrode 4015 is formedusing the same conductive film as that of the pixel electrode layer4030, and a terminal electrode 4016 is formed using the same conductivefilm as that of source and drain electrode layers of the thin filmtransistors 4010 and 4011.

The connecting terminal electrode 4015 is electrically connected to aterminal included in the FPC 4018 through an anisotropic conductive film4019.

Although FIGS. 12A to 12C illustrate an example in which the signal linedriver circuit 4003 is formed separately and mounted on the firstsubstrate 4001, the present invention is not limited to this structure.The scanning line driver circuit may be formed separately and thenmounted, or only a part of the signal line driver circuit or a part ofthe scanning line driver circuit may be formed separately and thenmounted.

FIG. 16 illustrates an example of a liquid crystal display module whichis formed as a liquid crystal display device disclosed in thisspecification.

FIG. 16 illustrates an example of the liquid crystal display module, inwhich an element substrate 2600 and a counter substrate 2601 areattached to each other with a sealant 2602, and an element layer 2603including a TFT or the like, a display element 2604 including a liquidcrystal layer, and an interlayer film 2605 including alight-transmitting chromatic-color resin layer that functions as a colorfilter are provided between the substrates to form a display region. Theinterlayer film 2605 including a light-transmitting chromatic-colorresin layer is necessary to perform color display. In the case of theRGB system, respective light-transmitting chromatic-color resin layerscorresponding to colors of red, green, and blue are provided forrespective pixels. The polarizing plate 2606 is provided on the outerside of the counter substrate 2601 and a polarizing plate 2607 and adiffuser plate 2613 are provided on the outer side of the elementsubstrate 2600. A light source includes a cold cathode tube 2610 and areflective plate 2611, and a circuit substrate 2612 is connected to awiring circuit portion 2608 of the element substrate 2600 through aflexible wiring board 2609 and includes an external circuit such as acontrol circuit and a power source circuit. As the light source, a whitediode may be used. The polarizing plate and the liquid crystal layer maybe stacked with a retardation plate interposed therebetween.

Through the above process, a highly reliable liquid crystal displaypanel as a liquid crystal display device can be manufactured.

This embodiment can be implemented in combination with any of thestructures disclosed in other embodiments as appropriate.

Embodiment 11

A liquid crystal display device disclosed in this specification can beapplied to a variety of electronic appliances (including game machines).As the electronic appliances, for example, there are a television device(also called a television or a television receiver), a monitor for acomputer or the like, a camera such as a digital camera or a digitalvideo camera, a digital photo frame, a mobile phone (also called amobile phone or a mobile telephone device), a portable game console, aportable information terminal, an audio playback device, and a largegame machine such as a pachinko machine.

FIG. 13A illustrates an example of a television device 9600. A displayportion 9603 is incorporated in a housing 9601 of the television device9600. The display portion 9603 can display images. Here, the housing9601 is supported on a stand 9605.

The television device 9600 can be operated by an operation switch of thehousing 9601 or a separate remote controller 9610. The channel andvolume can be controlled with operation keys 9609 of the remotecontroller 9610 and the images displayed on the display portion 9603 canbe controlled. Moreover, the remote controller 9610 may have a displayportion 9607 on which the information outgoing from the remotecontroller 9610 is displayed.

Note that the television device 9600 is provided with a receiver, amodem, and the like. With the receiver, general television broadcastingcan be received. Moreover, when the display device is connected to acommunication network with or without wires via the modem, one-way (froma sender to a receiver) or two-way (e.g., between a sender and areceiver or between receivers) information communication can beperformed.

FIG. 13B illustrates an example of a digital photo frame 9700. Forexample, a display portion 9703 is incorporated in a housing 9701 of thedigital photo frame 9700. The display portion 9703 can display a varietyof images, for example, displays image data taken with a digital cameraor the like, so that the digital photo frame can function in a mannersimilar to a general picture frame.

Note that the digital photo frame 9700 is provided with an operationportion, an external connection terminal (such as a USB terminal or aterminal which can be connected to a variety of cables including a USBcable), a storage medium inserting portion, and the like. They may beincorporated on the same plane as the display portion; however, they arepreferably provided on a side surface or the rear surface of the displayportion because the design is improved. For example, a memory includingimage data taken with a digital camera is inserted into the storagemedium inserting portion of the digital photo frame and the image datais imported. Then, the imported image data can be displayed on thedisplay portion 9703.

The digital photo frame 9700 may send and receive informationwirelessly. Via wireless communication, desired image data can bewirelessly imported into the digital photo frame 9700 and displayed.

FIG. 14A illustrates a portable game console including a housing 9881and a housing 9891 which are jointed with a connector 9893 so as to beopened and closed. A display portion 9882 and a display portion 9883 areincorporated in the housing 9881 and the housing 9891, respectively. Theportable game console illustrated in FIG. 14A additionally includes aspeaker portion 9884, a storage medium inserting portion 9886, an LEDlamp 9890, an input means (operation keys 9885, a connection terminal9887, a sensor 9888 (having a function of measuring force, displacement,position, speed, acceleration, angular speed, rotational frequency,distance, light, liquid, magnetism, temperature, chemical substance,sound, time, hardness, electric field, current, voltage, electric power,radiation, flow rate, humidity, gradient, vibration, smell, or infraredray), and a microphone 9889), and the like. Needless to say, thestructure of the portable game console is not limited to the above, andmay be any structure which is provided with at least a liquid crystaldisplay device disclosed in this specification. Moreover, anotheraccessory may be provided as appropriate. The portable game consoleillustrated in FIG. 14A has a function of reading a program or datastored in a storage medium to display it on the display portion, and afunction of sharing information with another portable game console viawireless communication. The portable game console of FIG. 14A can have avariety of functions other than those above.

FIG. 14B illustrates an example of a slot machine 9900, which is a largegame machine. A display portion 9903 is incorporated in a housing 9901of the slot machine 9900. The slot machine 9900 additionally includes anoperation means such as a start lever or a stop switch, a coin slot, aspeaker, and the like. Needless to say, the structure of the slotmachine 9900 is not limited to the above and may be any structure whichis provided with at least a liquid crystal display device disclosed inthis specification. Moreover, another accessory may be provided asappropriate.

FIG. 15A illustrates an example of a mobile phone 1000. The mobile phone1000 includes a housing 1001 in which a display portion 1002 isincorporated, and moreover includes an operation button 1003, anexternal connection port 1004, a speaker 1005, a microphone 1006, andthe like.

Information can be input to the mobile phone 1000 illustrated in FIG.15A by touching the display portion 1002 with a finger or the like.Moreover, calling or text messaging can be performed by touching thedisplay portion 1002 with a finger or the like.

There are mainly three screen modes of the display portion 1002. Thefirst mode is a display mode mainly for displaying images. The secondmode is an input mode mainly for inputting information such as text. Thethird mode is a display-and-input mode in which two modes of the displaymode and the input mode are mixed.

For example, in the case of calling or text messaging, the displayportion 1002 is set to a text input mode mainly for inputting text, andtext input operation can be performed on a screen. In this case, it ispreferable to display a keyboard or number buttons on almost the entirescreen of the display portion 1002.

When a detection device including a sensor for detecting inclination,such as a gyroscope or an acceleration sensor, is provided inside themobile phone 1000, display on the screen of the display portion 1002 canbe automatically switched by judging the direction of the mobile phone1000 (whether the mobile phone 1000 is placed horizontally or verticallyfor a landscape mode or a portrait mode).

Further, the screen modes are switched by touching the display portion1002 or operating the operation button 1003 of the housing 1001.Alternatively, the screen modes can be switched depending on kinds ofimages displayed on the display portion 1002. For example, when a signalfor an image displayed on the display portion is data of moving images,the screen mode is switched to the display mode. When the signal is textdata, the screen mode is switched to the input mode.

Further, in the input mode, a signal is detected by an optical sensor inthe display portion 1002 and if input by touching the display portion1002 is not performed for a certain period, the screen mode may becontrolled so as to be switched from the input mode to the display mode.

The display portion 1002 can also function as an image sensor. Forexample, an image of a palm print, a fingerprint, or the like is takenby touching the display portion 1002 with the palm or the finger,whereby personal authentication can be performed. Moreover, when abacklight or sensing light source which emits near-infrared light isprovided in the display portion, an image of finger veins, palm veins,or the like can be taken.

FIG. 15B also illustrates an example of a mobile phone. The mobile phoneillustrated in FIG. 15B includes a display device 9410 having a displayportion 9412 and operation buttons 9413 in a housing 9411 and acommunication device 9400 having scan buttons 9402, an external inputterminal 9403, a microphone 9404, a speaker 9405, and a light-emittingportion 9406 which emits light when receiving a call in a housing 9401.The display device 9410 having a display function can be detached fromor attached to the communication device 9400 having a telephone functionin two directions indicated by the arrows. Accordingly, the displaydevice 9410 and the communication device 9400 can be attached to eachother along their short sides or long sides. In addition, when only thedisplay function is needed, the display device 9410 can be detached fromthe communication device 9400 and used alone. Images or inputinformation can be transmitted or received by wireless or wirecommunication between the communication device 9400 and the displaydevice 9410, each of which has a rechargeable battery.

This application is based on Japanese Patent Application serial no.2008-308787 filed with Japan Patent Office on Dec. 3, 2008, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A liquid crystal display device comprising: atransistor over a substrate, the transistor comprising: a gateelectrode; a gate insulating film over the gate electrode; a first oxidesemiconductor layer over the gate electrode, the first oxidesemiconductor layer comprising indium, gallium, and zinc; a second oxidesemiconductor layer over the first oxide semiconductor layer, the secondoxide semiconductor layer comprising indium, gallium, and zinc; and asource electrode layer and a drain electrode layer over the second oxidesemiconductor layer; a first insulating film over the transistor, thefirst insulating film comprising a first opening; a resin layer over thetransistor, the resin layer comprising a second opening; a firstelectrode layer over the resin layer; a second insulating film over thefirst electrode layer; a second electrode layer over the secondinsulating film; a liquid crystal layer; and a spacer, wherein one ofthe first electrode layer and the second electrode layer is a pixelelectrode layer which is directly connected to the transistor throughthe first opening and the second opening, wherein the other of the firstelectrode layer and the second electrode layer is a common electrodelayer, wherein the first electrode layer and the second electrode layercomprise the same material, wherein a thickness of the first oxidesemiconductor layer is different from a thickness of the second oxidesemiconductor layer, wherein the first oxide semiconductor layer and thespacer overlap with each other, wherein the second oxide semiconductorlayer and the spacer overlap with each other, and wherein the liquidcrystal display device is configured to display an image by a lateralelectric field mode.
 2. The liquid crystal display device according toclaim 1, wherein the gate electrode comprises a copper layer and atitanium layer overlapping with the copper layer.
 3. The liquid crystaldisplay device according to claim 1, wherein the resin layer is alight-transmitting chromatic-color resin layer.
 4. The liquid crystaldisplay device according to claim 1, wherein the second electrode layercomprises a slit.
 5. The liquid crystal display device according toclaim 1, wherein the lateral electric field mode is an FFS mode.
 6. Aliquid crystal display device comprising: a transistor over a substrate,the transistor comprising: a gate electrode; a gate insulating film overthe gate electrode; a first oxide semiconductor layer over the gateelectrode, the first oxide semiconductor layer comprising indium,gallium, and zinc; a second oxide semiconductor layer over the firstoxide semiconductor layer, the second oxide semiconductor layercomprising indium, gallium, and zinc; and a source electrode layer and adrain electrode layer over the second oxide semiconductor layer; a firstinsulating film over the transistor, the first insulating filmcomprising a first opening; a resin layer over the transistor, the resinlayer comprising a second opening; a first electrode layer over theresin layer; a second insulating film over the first electrode layer; asecond electrode layer over the second insulating film; a liquid crystallayer; a spacer; a first connecting terminal electrode formed from thesame conductive film as a pixel electrode layer; and a second connectingterminal electrode formed from the same conductive film as the sourceelectrode layer and the drain electrode layer, wherein one of the firstelectrode layer and the second electrode layer is the pixel electrodelayer which is directly connected to the transistor through the firstopening and the second opening, wherein the other of the first electrodelayer and the second electrode layer is a common electrode layer,wherein the first electrode layer and the second electrode layercomprise the same material, wherein a thickness of the first oxidesemiconductor layer is different from a thickness of the second oxidesemiconductor layer, wherein the first oxide semiconductor layer and thespacer overlap with each other, wherein the second oxide semiconductorlayer and the spacer overlap with each other, and wherein the liquidcrystal display device is configured to display an image by a lateralelectric field mode.
 7. The liquid crystal display device according toclaim 6, wherein the gate electrode comprises a copper layer and atitanium layer overlapping with the copper layer.
 8. The liquid crystaldisplay device according to claim 6, wherein the resin layer is alight-transmitting chromatic-color resin layer.
 9. The liquid crystaldisplay device according to claim 6, wherein the second electrode layercomprises a slit.
 10. The liquid crystal display device according toclaim 6, wherein the lateral electric field mode is an FFS mode.